Concept for slurry separation and biogas production

ABSTRACT

The present invention concerns an anaerobic digestion of animal manures, energy crops and similar organic substrates. The process is capable of refining nutrients comprised in the digested biomass to fertilizers of commercial quality. The invention also provides a method for oprocessing animal carcasses or fractions thereof including meat and bone meal etc., with the objective of providing an alternative means for processing the organic waste material of animal origin while at the same time facilitating the production of fertilizers. The risk of spreading BSE prions or any other prions to animals or humans is thus substantially reduced if not eliminated. The biogas and slurry separation system according to the present invention is preferably integrated with the operations of animal husbandries into a total concept in which the internal and external performances of animal husbandries are optimised. The internal performances concern quality aspects related to the management of the animal houses and include industrial hygiene, animal welfare, gaseous and dust emissions and food safety. The external performances concern mainly energy production and emissions to the environment of nutrients and greenhouse gases and the sale of high quality food product.

TECHNICAL FIELD OF THE INVENTION

In a first aspect, the present invention concerns an anaerobic digestionof animal manures, energy crops and similar organic substrates. Theprocess is capable of refining nutrients comprised in the digestedbiomass to fertilizers of commercial quality. The biogas and slurryseparation system according to the present invention is preferablyintegrated with the operations of animal husbandries into a totalconcept in which the internal and external performances of animalhusbandries are optimised.

One additional aspect of the invention is the possible application fordisposing off animal waste in the form of animal carcasses,slaughterhouse waste, meat and bone meal, etc. The waste is refined inthe plant to fertilizers to be applied to agricultural land. A possiblecontent of BSE-prions or other prions is substantially reduced if noteliminated in the whole process. The animal produce is in this conceptnot used as fodder but fertilizer. The destruction of possible BSEprions in the biomass treated in the plant in combination with the useof the refined biomass as fertilizer in stead of fodder substantiallyreduces if not eliminates the risk of infecting animals or humans withBSE-prions or modifications thereof.

The internal performances concern quality aspects related to themanagement of the animal houses and include industrial hygiene, animalwelfare, control of gaseous and dust emissions and food safety. Theexternal performances concern mainly energy production and control ofemissions to the environment of nutrients and greenhouse gasses and thesale of high quality food products as well as an alternative way fordisposing of animal carcasses and the like.

BACKGROUND OF THE INVENTION Ammonia Stripping

The chemistry of ammonia is well known and stripping of ammonia fromdifferent fluids is a well known industrial process. It has for examplebeen employed by the sugar industry (Bunert et al. 1995; Chacuk et al.1994; Benito and Cubero 1996) and by municipalities as treatment oflandfill reject (Cheung et al. 1997). Ammonia may also be stripped frompig slurry based on the same principles as in the industry (Liao et al.1995).

The basic principle for large scale stripping of ammonia is increasingpH and aerating and heating of the wastewater or the slurry. It is oftenCa(OH)₂ or CaO which is used to increase pH. Other bases may be employedsuch as NaOH or KOH. The lime, however, is used on an industrial scaleby for instance the cement industry and is therefore cheap and readilyavailable as bulk ware.

Where the stripped ammonia is absorbed and an ammonia concentrate isproduced sulphuric acid is often used in the absorption column.Sulphuric acid is an industrial bulk ware and is available in atechnical quality appropriate for use in absorption columns strippingammonia from slurry and other waste waters (e.g. Sacuk et al. 1994).

Based on the experience gained in the sugar industry it has been foundthat the most appropriate parameter values are: Temperature 70° C.; a pHin the range of about 10-12; and a liquid gas ration of 1:800, 96%affectivity.

For stripping of ammonia from slurry it is found that the optimalparameter values at low temperature are: temperature 22° C.; pH of about10-12; liquid gas ratio of 1:2000, 90% affectivity, 150 h operation(Liao et al. 1995).

REFERENCES

-   Benito G. G. and Cubero M. T. G. (1996) Ammonia elimination from    beet sugar factory condensate streams by a stripping-reabsorbing    system. Zuckerindustrie 121, 721-726.-   Bunert U., Buczys R., Bruhns M., and Buchholz K. (1995) Ammonia    stripping. Zuckerindustrie 120, 960-969.-   Chacuk A., Zarzycki R., and Iciek J. (1994) A mathematical model of    absorption stripping columns for removal of ammonia from    condensates. Zuckerindustrie 119, 1008-1015.-   Cheung K. C., Chu L. M., and Wong M. H. (1997) Ammonia stripping as    a pretreatment for landfill leachate. Water Air and Soil Pollution    94, 209-221.-   Liao, P. H., Chen A., and Lo K. V. (1995) Removal of nitrogen from    swine manure wastewaters by ammonia stripping. Biotechnology &    Applied Microbiology 54, 1720.    Alkali and Thermal Hydrolyses

Thermal pre-treatment of biomass before anaerobic digestion is atechnology which is well described in the literature, e.g. Li and Noike(1992). In resent years thermal pre-treatment of municipal waste hasalso been used on a commercial scale by Cambi A S, Billingstad, Norway.

Wang et al. (1997a and b) found that thermal pre-treatment of municipalwaste at 60° C. and a hydraulic residence time of 8 days resulted in anincreased methane production of 52.1%. A similar result was found byTanaka et al. (1997), the combination however with alkali hydrolysesgave the highest increase in gas yield (200%). McCarty et al. haveperformed a series of studies showing that the combination of thermaland alkali hydrolysis increases the gas yield substantially. The pHhowever, shall be about 10 to 12, and preferably 11 or higher, beforethe chemical hydrolysis shall produce a significant additional gasyield.

The results of Wang et al. (1997) shows that the default parametervalues for ammonia stripping under section 2.1 (the pH of about 10 to12, preferably 11 or more, and the temperature of about 70° C. or moreduring a week) will increase the gas yield.

REFERENCES

-   Li Y. Y., and Noike T. (1992) Upgrading of anaerobic digestion of    waste activated sludge by thermal pre-treatment. Water Science and    Technology 26, 3-4.-   McCarty P. L., Young L. Y., Gossett J. M., Stuckey D. C., and Healy    Jr. J. B. Heat treatment for increasing methane yield from organic    materials. Stanford University, California 94305, USA.-   Tanaka S., Kobayashi T. Kamiyama K. and Bildan M. L. N. S. (1997)    Effects of thermo chemical pre-treatment on the anaerobic digestion    of waste activated sludge. Water Science and Technology 35, 209-215.-   Wang Q., Noguchi C., Hara Y., Sharon C., Kakimoto K., and Kato Y.    (1997a) Studies on anaerobic digestion mechanisms: Influence of    pre-treatment temperature on biodegradation of waste activated    sludge. Environmental Technology 18, 999-1008.-   Wang Q., Noguchi C. K., Kuninobu M., Hara Y., Kakimoto K.    Ogawa H. I. And Kato Y. (1997b) Influence of hydraulic retention    time on anaerobic digestion of pre-treated sludge. Biotechnology    Techniques 11, 105-108.    Sanitation

Sanitation of slurry before transporting and field applicationconstitute an important strategy for reducing the risk of spreading zoonoses and veterinary vira, bacteria and parasites (e.g. Bendixen 1999).Anaerobe digestion has proven effective in reducing the number of zoonoses in slurries but it does not eliminate these organisms (Bendixen1999; Pagilla et al. 2000). The use of CaO for sanitation of sewagesludge has also shown that Ascaris eggs and parasites (Eriksen et al.1996) and virus are reduced substantially but not completely (Turner andBurton 1997).

REFERENCES

-   Bendixen H. J. Hygienic safety—results of scientific investigations    in Denmark (sanitation requirements in Danish biogas plants).    Hohenheimer Seminar IEA Bioenergy Workshop March 1999.-   Eriksen L., Andreasen P. Ilsoe B. (1996) Inactivation of Ascaris    suum eggs during storage in lime treated sewage sludge. Water    Research 30, 1026-1029.-   Pagilla K. R., Kim H., and Cheunbarn T. (2000) Aerobic thermopile    and anaerobic mesopile treatment of swine waste. Water Research 34,    2747-2753.-   Turner C. and Burton C. H. (1997) The inactivation of viruses in pig    slurries: a review. Bioresource Technology 61, 9-20.    Foam

Foam formation associated with anaerobic digestion may constitute aserious problem for operating the fermentors. A number of substances forremediation of foam are commercially available including differentpolymers, plant oils (e.g. rape oil) and different salts (e.g.Vardar-Sukan 1998). However, polymers may cause environmental concernsand are often expensive and ineffective.

REFERENCES

-   Vardar-Sukan F. (1998) Foaming: consequences, prevention and    destruction. Biotechnology Advances 16, 913-948.    Flocculation

Calcium-ions are a well known as means to flocculate substances andparticles due to the formation of calcium-bridges between organic andinorganic substances in solution or suspension thus forming “flocks” ofparticles (e.g. Sanin and Vesilind 1996). For this reason calcium hasbeen used for dewatering of sewage sludge (Higgins and Novak 1997).

REFERENCES

-   Higgins M. J. and Novak J. T. (1997). The effects of cat ions on the    settling and de-watering of activated sludge's: Laboratory results.    Water Environment Research 69, 215-224.-   Sanin F. D., and Vesilind P. A. (1996) Synthetic sludge: A    physical/chemical model in understanding bio flocculation. Water    Environment Research 68, 927-933.    Decanter Centrifuge Slurry Separation, P Stripping

Decanter centrifuges have been applied to a number of industrialprocesses during the last 100 years.

Among recent examples of the use of decanter centrifuges is the NovoNordisk plant in Kalundborg where all waste from the large insulinfermentation units is treated. Also municipal sludge is dewatered bymeans of decanter centrifuges (Alfa Laval A/S). The decanter centrifugesseparate the dry (solid) matter from the sludge or wastes, while thewater phase or the reject water is lead to a conventional sewagetreatment plant.

Experiments with separation of cattle, pig and degassed slurry showfirstly that decanter centrifuges can treat all manures without anydifficulties. It has also been found that the centrifuges removeapproximately 70% dry matter, 60-80% total P and only 14% of total Nfrom a slurry previously digested thermopile (Møller et al. 1999; Møller2000a). The corresponding values for raw slurry from cattle and pigswere somewhat lower. It should be noted that only 14% of total N isremoved from the waste.

The total treatment cost has been calculated to 5 Dkr. per m³ slurry ata slurry volume of 20.000 tons or more. In those situations where theslurry volume exceeds 20.000 tons the decanter centrifuges are costefficient and cheap instruments for separation of dry matter and total Pfrom slurry (Møoller et al. 1999).

Under normal circumstances it is without any interest to treat slurry ina decanter centrifuge, because it is not associated with any volumereduction or other advantages to the farmers. The ammonia loss followingfield application of treated slurry may be somewhat reduced due to anincreased infiltration rate into the soil (Møller 2000b), but this is byfar sufficient incentive to farmers for use of decanter centrifuges.

REFERENCES

-   Møller H. B. (2000a) Opkoncentrering af næringsstoffer i    husdyrgødning med dekantercentrifuge og skruepresse. Notat 12.    September 2000, Forskningscenter Bygholm.-   Møller H. B. (2000b) Gode resultater med at separere gylle.    Maskinbladet 25. august 2000.

Møller H. B., Lund I., and Sommer S. G. (1999) Solid-liquid separationof livestock slurry: efficiency and cost.

-   Alfa Laval A/S Gylleseparering. Separeringsresultater med    decantercentrifuge.    P-Precipitation

Dissolved P is precipitated almost immediately following addition of Caas calcium phosphate Ca₃(PO₄)₂ (Cheung et al. 1995).

REFERENCES

-   Cheung K. C., Chu L. M., and Wong M. H. (1997) Ammonia stripping as    a pretreatment for landfill leachate. Water Air and Soil Pollution    94, 209-221.    Prevention of Struvite Formation

It is an additional important aspect that the P precipitation incombination with the stripping of ammonia prevents the formation ofstruvite (MgNH₄PO₄). Struvite constitutes a significant working problemin heat-exchangers, transport in pipes, etc. (Krüger 1993). Themechanism is P-removal through formation of CaPO₄ as well as removal ofammonia through the stripping process. The P and ammonia removalprevents formation of struvite.

-   Krüger (1993) Struvit dannelse i biogasfeellesanlæg. Krüger    WasteSystems AS.    Reject Water Filtration

Systems for final treatment and membrane filtration of reject water havebeen presented over the past 10 years in the form of e.g. membraneplants (BioScan A/S, Ansager ApS) and plants based on steam compression(Funki A/S, Bjørnkjær Maskinfabrikker A/S). These systems generallyresult in a gross cost per m³ slurry of 50-100 Dkr. The plants arefurther not able to treat other types of manure but pig slurry.

The reduction of volume obtained by these plants is often not more than50-60%, meaning that field application of the remains in any casedepends on conventional devices. Hence, these plants are not competitivedue to the cost level and/or a limited volume reduction.

However, it is important to consider and recognise the cost level ofthese plants. It is also valuable to consider the energy use in the formelectricity which the mechanical steam compression gives rise to, i.e.about 50 kWh per tons treated slurry. This means that membranes, underthe assumption that the water phase to be filtered consists of salts andminimal amounts of dry matter only, which do not produce scaling orfouling problems, may be able to out compete evaporation technologies.

REFERENCES

-   Argaman Y. (1984) Single sludge nitrogen removal in an oxidation    ditch. Water Research 18, 1493-1500.-   Blouin M., Bisaillon J. G., Beudet R., and Ishague M. (1988) Aerobic    biodegradation of organic matter of swine waste. Biological Wastes    25, 127-139.-   Bouhabila E. H., Aim R. B., and Buisson H. (1998) Micro filtration    of activated sludge using submerged membrane with air bubbling    (application to wastewater treatment). Desalination 118, 315-322.-   Burton C. H., Sneath R. W., Misselbrook T. H., and Pain B. F. (1998)    Journal of Agricultural Engineering Research 71, 203.-   Camarro L., Diaz J. M. and Romero F. (1996) Final treatments for    anaerobically digested piggery effluents. Biomass and Bioenergy 11,    483-489.-   Doyle Y. and de la Noüe J. (1987) Aerobic treatment of swine manure:    Physicochemical aspects. Biological Wastes 22, 187-208.-   Engelhardt N., Firk W., and Wamken W (1998) Integration of membrane    filtration into the activated sludge process in municipal wastewater    treatment. Water Science and Technology 38, 429-436.-   Garraway J. L. (1982) Investigations on the aerobic treatment of pig    slurry. Agricultural Wastes 4,131-142.-   Ginnivan M. J. (1983) The effect of aeration on odour and solids of    pig slurries. Agricultural Wastes 7,197-207.-   Gönenc I. E. and Harremoës P. (1985) Nitrification in rotating disc    systems-I. Criteria for transition from oxygen to ammonia rate    limitation. Water Research 19, 1119-1127.-   Scott J. A.; Neilson D. J. Liu W., and Boon P. N. (1998) A dual    function membrane bioreactor system for enhanced aerobic remediation    of high-strength industrial waste. Water Science and Technology 38,    413-420.-   Silva C. M., Reeve D. W., Husain H., Rabie H. R., and    Woodhouse K. A. (2000) Journal of Membrane Science 173, 87-98.-   Visvanathan C., Yang B-S., Muttamara S., and Maythanukhraw R. (1997)    Application of air back flushing in membrane bioreactor. Water    Science and Technology 36, 259-266.-   Zaloum R., Coron-Ramstrim A.-F. Gehr R. (1996) Final clarification    by integrated filtration within the activated sludge aeration tank.    Environmental Technology 17, 1007-1014.    Lime Cooking

A thermal and chemical hydrolysis at temperatures less than 100° C. andtherefore pressures at about 1 atm represents one option for increasingthe availability of the organic matter for biogas generation. However,the complex carbohydrates such as cellulose, hemicelluloses and ligninis not completely hydrolysed by such treatments. Fibres from straw,maize and other crops are not made available for methane formation bysuch treatments (Bjerre et al 1996; Schmidt and Thomsen 1998; Thomsenand Schmidt 1999; Sirohi and Rai 1998). An alkali lime cooking atmoderate temperatures above 100° C. is well suited to render thesesubstrates available to microbial decomposition (Curelli et al. 1997;Chang et al. 1997; Chang et al. 1998).

This treatment, when applied to cellulose fibres from sugar cane cut to0.5 mm (with 4% CaO, 200° C. and 16 bar), disintegrates the cellulose tosmall organic acids as formic acid, acetic acid, lactic acid etc. Themethane generation from treated cellulose is thus as high as 70% of thecorresponding amount of carbohydrates as pure glucose (Azzam and Naser1993). Also, green crops can be treated in a lime cooker, but at lowertemperatures. It has been shown that the optimal result was achievedwhen water hyacinths were exposed to pH 11 and 121° C. (Patel et al.1993).

Formation of PAH and of substances inhibitory to methane bacteria may beformed at elevated temperatures (Varhegyi et al. 1993; Patel et al.1993). However, this phenomena has not been seen at the relativelymoderate temperatures used in lime cooking as compared the pyrolysis(Azzam et al. 1993). During pyrolysis the temperatures are so high thatthe biomass disintegrates directly to gasses as hydrogen, methane andcarbon monoxide but unfortunately also to PAH and other pollutants.

REFERENCES

-   Azzam A. M. and Nasr M. I. (1993) Physicothermochemical    pre-treatments of food processing waste for enhancing anaerobic    digestion and biogas fermentation. Journal of Environmental Science    and Engineering 28, 1629-1649.-   Bjerre A. B., Olesen A. B., Fernquist T., Ploger A.,    Schmidt A. S. (1996) Pretreatment of wheat straw using combined wet    oxidation and alkaline hydrolysis resulting in convertible cellulose    and hemicelluloses. Biotechnology and Bioengineering 49, 568-577.-   Chang V. S., Nagwani M., Holtzapple M. T. (1998) Original    articles—Lime pretreatment of crop residues bagasse and wheat straw.    Applied Biochemistry and Biotechnology Part A—Enzyme Engineering and    Biotechnology 74, 135-160.-   Chang V. S., Barry B., Holtzapple M. T. (1997) Lime pre-treatment of    switchgrass. Applied Biochemistry and Biotechnology Part A—Enzyme    Engineering and Biotechnology 63-65, 3-20.-   Curelli N., Fadda M. B., Rescigno A., Rinaldi A. C., soddu G.,    Sollai E., Vaccargiu S.; Sanjust E., Rinaldi A. (1997) Mild    alkaline/oxidative pretreatment of wheat straw. Process Biochemistry    32, 665-670.-   Patel V., Desai M., and Madamwar D. (1993) Thermo chemical    pre-treatment of water hyacinth for improved biomethanation. Applied    Biochemistry and Biotechnology 42, 67-74.-   Schmidt A. S. and Thomsen A. B. (1998) Optimisation of wet oxidation    pretreatment of wheat straw. Bioresource Technology 64, 139-152.-   Sirohi S. K. and Rai S. N. (1998) Optimisation of treatment    conditions of wheat straw with lime: Effect of concentration,    moisture content and treatment time on chemical composition and in    vitro digestibility. Animal Feed Science and Technology 74, 57-62.-   Thomsen A. B. and Schmidt A. S. (1999) Further development of    chemical and biological processes for production of bio ethanol:    optimisation of pre-treatment processes and characterisation of    products. Rise National Laboratory, Roskilde, Denmark.-   Varhegyi G., Szabo P., Mok W. S. L., and Antal M. J. (1993) Kinetics    of the thermal decomposition of cellulose in sealed vessels at    elevated pressures. Journal of Analytical and Applied Pyrolysis 26,    159-174.    Energy Crop Silage

The conventional use of energy crops is mainly in the form of solid fuelfor burning (willow as wood chops, straw or whole seed) or as fuel forengines (rape oil). On an experimental basis beets and straw is used forproduction of ethanol (Parsby; Sims 2001; Gustavsson et al. 1995; Wymanand Goodman 1993; Kuch 1998). In other parts of the world the use ofenergy crops is widespread and subject to much research. The use ofterrestrial as well as marine and freshwater plants is well documented(Gunaseelan 1997; Jewell et al. 1993; Jarwis et al 1997). Some studieswould appear to indicate that anaerobic fermentation of energy crops iscompetitive to other uses of biomass (Chynoweth D. P., Owens J. M., andLegrand R. 2001).

The use of energy crops is well motivated. The use of straw is organisedin a way which probably makes this practise a concept to be seen for anumber of years to come. The use of wood chops seems to be economicaland practical viable. Incineration of grain cereals on the other handhas given rise to ethical objections. The production of grain cereals isalso inevitable associated with the use of fertilizers and pesticidesand N-losses from the fields. N is also lost during the burning of thebiomass.

REFERENCES

-   Beck J. Co-fermentation of liquid manure and beets as a regenerative    energy. University of Hohenheim, Dep. Agricultural Engineering and    Animal Production. Personal communication.-   Chynoweth D. P., Owens J. M., and Legrand R. (2001) Renewable    methane from anaerobic digestion of biomass. Renewable Energy 22,    1-8.-   Gunaseelan V. N. (1997) Anaerobic digestion of biomass for methane    production: A review. Biomass and Bioenergy 13, 83-114.-   Gustavsson L, Borjesson P., Bengt J., Svenningsson P. (1995)    Reducing CO₂ emissions by substituting biomass for fossil fuels.    Energy 20, 1097-1113.-   Jewell W. J., Cummings R. J., and Richards B. K. (1993) Methane    fermentation of energy crops: maximum conversion kinetics and in    situ biogas purification. Biomass and Bioenergy 5, 261-278.-   Jarvis Å., Nordberg Å., Jarlsvik T., Mathiesen B., and    Svensson B. H. (1997) Improvement of a grass-clover silage-fed    biogas process by the addition of cobalt. Biomass and Bioenergy 12,    453-460.-   Kuch P. J., Crosswhite W. M. (1998) The agricultural regulatory    framework and biomass production. Biomass and Bioenergy 14, 333-339.-   Parsby M. Halm og energiafgrøder—analyser af økonomi, energi og    miljø. Rapport Nr. 87, Statens Jordbrugs og Fiskeriøkonomiske    Institut.-   Sims R. H. E. (2001) Bioenergy—a renewable carbon sink. Renewable    Energy 22, 31-37.-   Wyman C. E. and Goodman B. J. (1993) Biotechnology for production of    fuels chemicals and materials from biomass. Applied Biochemistry and    Biotechnology 39, 41-59.-   Banks C. J. and Humphreys P. N. (1998) The anaerobic treatment of a    lignocellulosic substrate offering little natural pH buffering    capacity. Water Science and Technology 38, 29-35;-   Colleran E., Wilkie A., Barry M., Faherty G., O'kelly N. and    Reynolds P. J. (1983) One and two stage anaerobic filter digestion    of agricultural wastes. Third Int Symp. on Anaerobic Digestion, pp.    285-312, Boston Mass. (1983).-   Dugba P. N., and Zhang R. (1999) Treatment of dairy wastewater with    two-stage anaerobic sequencing batch reactor systems—thermopile    versus mesopile operatons. Bioresource Technology 68, 225-233.-   Ghosh S., Ombregt J. P., and Pipyn P. (1985) Methane production from    industrial wastes by two-phase digestion. Water Research 19,    1083-1088.-   Han Y., Sung S., and Dague R. R. (1997) Temperature-phased anaerobic    digestion of wastewater sludge's. Water Science and Technology 36,    367-374.-   Krylova N. I., Khabiboulline R. E., Naumova R. P. Nagel M. A. (1997)    The influence of ammonium and methods for removal during the    anaerobic treatment of poultry manure. Journal of Chemical    Technology and Biotechnology 70, 99-105.-   Hansen K. H., Angelidaki I., Ahring B. K. (1998) Anaerobic digestion    of swine manure: inhibition by ammonia. Water Research 32, 5-12.-   Kayhanian M. (1994) Performance of high-solids anaerobic digestion    process under various ammonia concentrations. Journal of Chemical    Technology and Biotechnology 59, 349-352.-   Wang Q., Noguchi C. K., Kuninobu M., Hara Y., Kakimoto K., Ogawa H.    I., and Kato Y. (1997) Influence of hydraulic retention time on    anaerobic digestion of pre-treated sludge. Biotechnology Techniques    11, 105-108.    Disposal Systems for Animal Cadavers etc.

The present disposal system for animal cadavers is organised byregistrating plants which are licensed to process the animal cadavers.The cadavers are primarily used for production of meat and bone mealwhich traditionally have been used for animal foodstuff.

The present BSE-crisis have stopped this practise by a regulatory orderfrom the EU-commission, stating that meat and bone meal cannot be usedas animal foodstuff.

The livestock sector and associated businesses in Europe thus face thechallenge to find alternative use of meat and bone meal or alternativeways of disposing off the meal. However, this is a difficult taskbecause of the constraints imposed by the risk of spreading BSE prionsor other prions possibly present in the meal or other fractions ofanimal cadavers.

The use of meat and bone meal or animal cadavers in conventional biogasplants is certainly not advisable and only partly possible. Theprocessing of animal cadavers in plants licensed to process such animalsis usually performed at temperatures around 130° C., with pressurearound 2-3 bar with a retention time of 20 min. Such conditions are notto be found in conventional biogas plants.

The below mentioned patents and patent applications form part of theprior art.

DE3737747 describes a plant and a process to stripping of N. CaO isadded to the manure by which the ammonia is stripped, said ammonia isabsorbed in a water solution containing hydrochloric acid. A number ofaspects of the invention are not described by this reference. Thisapplies, among other things, to the pre-treatment such as the alkalinehydrolysis, welfare in the animal houses, utilization of energy crops,absorbing of ammonia in a sulfur solution, the precipitation of P,prevention of struvite formation etc. and the use of biogas through alocal gas engine or through an established pipeline for natural gas.

DE4201166 describes a method of concurrent treatment of differentorganic waste products, in which the waste products are separated intothree fractions containing different amounts of solid components. Solidfractions are homogenised before fermentation and biogas production. Anumber of aspects of the invention are not described by this reference.This applies, among other things, to the pre-treatment such as thealkaline hydrolysis, welfare in the animal houses, utilization of energycrops, absorbing of ammonia in a sulfur solution, the precipitation ofP, prevention of struvite formation etc. and the use of biogas through alocal gas engine or through an established pipeline for natural gas.

DE4444032 describes a plant and a process in which slurry i the firstreactor is stirred, aerated and added lime to pH 9.5 to strip ammonia.In the second reactor a salt containing ferro and a polymer are added toneutralise the slurry and precipitate solids. A number of aspects of theinvention are not described by this reference. This applies, among otherthings, to the pre-treatment such as the alkaline hydrolysis, welfare inthe animal houses, utilization of energy crops, absorbing of ammonia ina sulfur solution, the precipitation of P, prevention of struviteformation etc. and the use of biogas through a local gas engine orthrough an established pipeline for natural gas.

DE196615063 describes a process in which ammonia is stripped fromfermented manure. A number of aspects of the invention are not describedby this reference. This applies, among other things, to thepre-treatment such as the alkaline hydrolysis, utilization of energicrops, the precipitation of P, prevention of struvite formation etc. andthe use of biogas through a local gas engine or through an establishedpipeline for natural gas.

EP0286115 describes a method to production of biogas in which manure isadded fat acids or compositions containing fat acids. A number ofaspects of the invention are not described by this reference. Thisapplies, among other things, to the pretreatment such as the alkalinehydrolysis, utilization of energi crops, the precipitation of P,prevention of struvite formation etc. and the use of biogas through alocal gas engine or through an established pipeline for natural gas.

EP0351922 describes a plant and a process in which the stripping ofammonia, carbon dioxide and phosphate occurs from liquid manure. Themanure is transported from the farm by tank cars to the plant where theslurry is treated with hot air and by that partly stripped of ammoniaand carbon dioxide. The remaining part of the slurry is heated and limeis added to pH 10-11, by which more ammonia is stripped and calciumphosphate is formed. The stripped ammonia is absorbed in an acidicsolution by the formation of ammonium salt, which is dried and utilizedas fertilizers. A decanter centrifuge is used to separate solid partsfrom the slurry. A number of aspects of the invention are not describedby this reference. This applies, among other things, to thepre-treatment such as the alkaline hydrolysis, welfare in the animalhouses, utilization of energi crops, prevention of struvite formationetc. and the use of biogas through a local gas engine or through anestablished pipeline for natural gas.

ES2100123 describes a plant and a process in which liquid manure iscleaned. Organic components is degraded and precipitated solids isremoved by decanter centrifugation. The liquid is added acid and isspread in the land or is further cleaned by aeration and by thatstripping of ammonia. The cleaned liquid is diverted to a waterpurifying plant. A number of aspects of the invention are not describedby this reference. This applies, among other things, to thepre-treatment such as the alkaline hydrolysis, welfare in the animalhouses, stripping of ammonia at an early step, utilization of energicrops, prevention of struvite formation etc. and the use of biogasthrough a local gas engine or through an established pipeline fornatural gas.

FR2576741 describes a process to the production of biogas by fermentingof liquid manure. The slurry is treated with lime and precipitatedcomponents is removed. A number of aspects of the invention are notdescribed by this reference. This applies, among other things, to thepretreatment such as the alkaline hydrolysis, utilization of energicrops, the precipitation of P, prevention of struvite formation etc. andthe use of biogas through a local gas engine or through an establishedpipeline for natural gas.

GB 2013170 describes a plant and a method to production of biogas. Inthe first reactor the organic material is acidified and the solidfraction is removed. The liquid fraction is diverted to the secondreactor in which an anaerobic degradation occurs with the production ofmethane gas. A number of aspects of the invention are not described bythis reference. This applies, among other things, to the pre-treatmentsuch as the alkaline hydrolysis, welfare in the animal houses, strippingof ammonia, utilization of energi crops, prevention of struviteformation etc. and the use of biogas through a local gas engine orthrough an established pipeline for natural gas.

DE19644613 describes a method to produce solid fertilisers from manure.The liquid manure is added substrate from the biogas production togetherwith CaO or Ca(OH)₂. The stripped ammonia is collected. A number ofaspects of the invention are not described by this reference. Thisapplies, among other things, to the pretreatment such as the alkalinehydrolysis, utilization of energi crops, the precipitation of P,prevention of struvite formation etc. and the use of biogas through alocal gas engine or through an established pipeline for natural gas.

DE19828889 describes co-fermentation of harvested crops and organicwaste with the production of biogas. The material is homogenised andfermented. A number of aspects of the invention are not described bythis reference. This applies, among other things, to the pre-treatmentsuch as the alkaline hydrolysis, utilization of energi crops, theprecipitation of P, prevention of struvite formation etc. and the use ofbiogas through a local gas engine or through an established pipeline fornatural gas.

U.S. Pat. No. 4,041,182 describes a method to production of animalfoodstuff from organic waste. A number of aspects of the invention arenot described by this reference. This applies, among other things, tothe pre-treatment such as the alkaline hydrolysis, utilization of energicrops, the precipitation of P, prevention of struvite formation etc. andthe use of biogas through a local gas engine or through an establishedpipeline for natural gas.

U.S. Pat. No. 4,100,023 describes a plant and a process to theproduction of methane gas and fertilisers. In the first reactor an aerobdegradation of the homogenised material is performed. In the secondreactor which is heated, an anaerob degradation and the biogasproduction occurs. Fertilisers are produced as liquids. A number ofaspects of the invention are not described by this reference. Thisapplies, among other things, to the pre-treatment such as the alkalinehydrolysis, welfare in the animal houses, stripping of ammonia,utilization of energi crops, prevention of struvite formation etc. andthe use of biogas through a local gas engine or through an establishedpipeline for natural gas.

U.S. Pat. No. 4,329,428 describes a plant for anaerobic decomposition,in particular material from various green plants, and the use of theproduced biogas. The plant is based on the decomposition and caused bymesofilic or thermopile anaerobic bacteria. A number of aspects of theinvention are not described by this reference. This applies, among otherthings, to the pre-treatment such as the alkaline hydrolysis, thestripping of ammonia, the precipitation of P, prevention of struviteformation etc. and the use of biogas through a local gas engine orthrough an established pipeline for natural gas.

U.S. Pat. No. 4,579,654 describes a plant and a process to producebiogas from organic materials. Solid materials are hydrolysed, acidifiedand fermented. A number of aspects of the invention are not described bythis reference. This applies, among other things, to the pre-treatmentsuch as the alkaline hydrolysis, welfare in the animal houses, strippingof ammonia, utilization of energi crops, prevention of struviteformation etc. and the use of biogas through a local gas engine orthrough an established pipeline for natural gas.

U.S. Pat. No. 4,668,250 describes a process in which ammonia is removedfrom the liquid fraction by aeration. A number of aspects of theinvention are not described by this reference. This applies, among otherthings, to the pre-treatment such as the alkaline hydrolysis,utilization of energi crops, the precipitation of P, prevention ofstruvite formation etc. and the use of biogas through a local gas engineor through an established pipeline for natural gas.

U.S. Pat. No. 4,750,454 describes a plant for anaerobic digestion ofanimal manure and the use of the biogas produced by the process. Theplant is based on decomposition caused by mesofilic or thermopileanaerobic bacteria and utilizes a local gas powdered engine equippedwith a generator. A number of aspects of the invention are not describedby this reference. This applies, among other things, to the pretreatmentsuch as the alkaline hydrolysis, the stripping of ammonia, theprecipitation of P, prevention of struvite formation etc. and the use ofbiogas through a local gas engine or through an established pipeline fornatural gas.

U.S. Pat. No. 5,071,559 describes a method to treatment of manure. Themanure is added water and the mixture is acidified. Liquid is removed bysteamproduction, which again is condensated in another reactor andtreated anaerobic to produce biogas. The fermented liquid is fraction isthen treated by an aerob process. A number of aspects of the inventionare not described by this reference. This applies, among other things,to the pre-treatment such as the alkaline hydrolysis, welfare in theanimal houses, stripping of ammonia, utilization of energi crops,prevention of struvite formation etc. and the use of biogas through alocal gas engine or through an established pipeline for natural gas.

U.S. Pat. No. 5,296,147 describes a process to treat manure and otherorganic components. The organic waste fermentes and is then nitrifiedand further denitrified. A number of aspects of the invention are notdescribed by this reference. This applies, among other things, to thepre-treatment such as the alkaline hydrolysis, welfare in the animalhouses, stripping of ammonia, utilization of energi crops, prevention ofstruvite formation etc. and the use of biogas through a local gas engineor through an established pipeline for natural gas.

U.S. Pat. No. 5,389,258 describes a method to production of biogas fromsemi-solid and solid organic waste. A number of aspects of the inventionare not described by this reference. This applies, among other things,to the pre-treatment such as the alkaline hydrolysis, welfare in theanimal houses, stripping of ammonia, utilization of energi crops,prevention of struvite formation etc. and the use of biogas through alocal gas engine or through an established pipeline for natural gas.

U.S. Pat. No. 5,494,587 describes a process with a catalytic treatmentof manure including reduction of the nitrogen concentration. A number ofaspects of the invention are not described by this reference. Thisapplies, among other things, to the pre-treatment such as the alkalinehydrolysis, welfare in the animal houses, stripping of ammonia,utilization of energi crops, prevention of struvite formation etc. andthe use of biogas through a local gas engine or through an establishedpipeline for natural gas.

U.S. Pat. No. 5,525,229 describes a general procedure for anaerobicdigestion of organic substrates under thermopile as well as mesofilicconditions.

U.S. Pat. No. 5,593,590 describes separation and treatment of liquid andsolid organic waste following a separation of the two fractions. Theliquid fraction is fermented with the production of biogas followed byremoving of precipitated solid components, which partly is recirculatedin the process. The solid fraction is treated in an aerob process and isproduced into compost, fertilisers or animal foodstuff. Part of theproduced biogas comprising methane and CO₂ is reuse to the reduction ofthe pH level in the liquid fraction by a CO2 absorption. Solids isprecipitated from liquid fractions e.g. by a decanter centrifuge, andammonia is stripped from the liquid by a pH of 9-10. Reject water can beused to clean stables. A number of aspects of the invention are notdescribed by this reference. This applies, among other things, to thepretreatment such as the alkaline hydrolysis, welfare in the animalhouses by use of straw, stripping of ammonia before biogas production,utilization of energi crops, prevention of struvite formation etc. andthe use of biogas through a local gas engine or through an establishedpipeline for natural gas.

U.S. Pat. No. 5,616,163 describes a method to treatment of manure bywhich nitrogen is utilised in the production of fertilisers. Liquidmanure is added CO2 and/or CaSO4 by which ammonia is stripped. A numberof aspects of the invention are not described by this reference. Thisapplies, among other things, to the pre-treatment such as the alkalinehydrolysis, welfare in the animal houses by use of straw, stripping ofammonia before biogas production, utilization of energi crops,prevention of struvite formation etc. and the use of biogas through alocal gas engine or through an established pipeline for natural gas.

U.S. Pat. No. 5,656,059 describes a method to treat manure by whichnitrogen is utilised in the production of fertilisers more or less bynitrification. A number of aspects of the invention are not described bythis reference. This applies, among other things, to the pre-treatmentsuch as the alkaline hydrolysis, welfare in the animal houses by use ofstraw, stripping of ammonia before biogas production, utilization ofenergi crops, prevention of struvite formation etc. and the use ofbiogas through a local gas engine or through an established pipeline fornatural gas.

U.S. Pat. No. 5,670,047 describes a general procedure for anaerobicdecomposition of organic substrates to gases.

U.S. Pat. No. 5,681,481 U.S. Pat. No. 5,783,073 and U.S. Pat. No.5,851,404 describes a process and an apparatus to stabilising of slurry.Lime is added to pH≧12 and the mass is heated to at least 50.degree.Cfor 12 hours. Ammonia is stripped, and is either discharged into theatmosphere or recirculated in the system. A ‘preheat chamber’ can beused as well as decanter centrifugation as well as mixing of the sludgeto keep it in a liquid condition. The sludge is spread to land. A numberof aspects of the invention are not described by this reference. Thisapplies, among other things, to the pre-treatment such as the alkalinehydrolysis, welfare in the animal houses by use of straw, stripping ofammonia before biogas production, utilization of energi crops,prevention of struvite formation etc. and the use of biogas through alocal gas engine or through an established pipeline for natural gas.

U.S. Pat. No. 5,746,919 describes a process in which organic waste istreated in a thermofil anaerob reactor followed by treatment in amesofil anaerob reactor. In both reactors a production of methane gasoccurs. A number of aspects of the invention are not described by thisreference. This applies, among other things, to the pre-treatment suchas the alkaline hydrolysis, welfare in the animal houses by use ofstraw, stripping of ammonia before biogas production, utilization ofenergi crops, prevention of struvite formation etc. and the use ofbiogas through a local gas engine or through an established pipeline fornatural gas.

U.S. Pat. No. 5,773,526 describes a process in which liquid and solidorganic waste is fermented first by a mesofil process and thereby by athermofil process. Solid components is hydrolysed and acidifies. Anumber of aspects of the invention are not described by this reference.This applies, among other things, to the pre-treatment such as thealkaline hydrolysis, welfare in the animal houses by use of straw,stripping of ammonia before biogas production, utilization of energicrops, prevention of struvite formation etc. and the use of biogasthrough a local gas engine or through an established pipeline fornatural gas.

U.S. Pat. No. 5,782,950 describes fermentation of biological waste by ahomogenisation, aeration and heating of the mass. The waste isfractionated into a liquid and a solid fraction. The solids is producedinto compost. The liquids is fermented by anaerob mesofil and thermofilprocess with production of biogas. Reject water is recirculated from thebiogas reactor to the homogenisation process. Reject water from thebiogas reactor is treated in a plant clarification installation. Anumber of aspects of the invention are not described by this reference.This applies, among other things, to the pre-treatment such as thealkaline hydrolysis, welfare in the animal houses, stripping of ammoniabefore biogas production, utilization of energi crops, prevention ofstruvite formation etc. and the use of biogas through a local gas engineor through an established pipeline for natural gas.

U.S. Pat. No. 5,853,450 describes a method to produce pasteurisedcompost from organic waste and green plant materials. The pH of theorganic is increased to 12 and heated to above 55.degree.C. When thegreen plant material is added pH is lowered to 7-9.5. The mixture isfermented. A number of aspects of the invention are not described bythis reference. This applies, among other things, to the pre-treatmentsuch as the alkaline hydrolysis, welfare in the animal houses, strippingof ammonia before biogas production, prevention of struvite formationetc. and the use of biogas through a local gas engine or through anestablished pipeline for natural gas.

U.S. Pat. No. 5,863,434 describes a method to stabilise organic waste bydegradation in a psychrofil anaerob process. A number of aspects of theinvention are not described by this reference. This applies, among otherthings, to the pre-treatment such as the alkaline hydrolysis, welfare inthe animal houses, stripping of ammonia before biogas production,prevention of struvite formation etc. and the use of biogas through alocal gas engine or through an established pipeline for natural gas.

U.S. Pat. No. 6,071,418 describes a method and a system to treat manurewith zone in a way that induces an aerob and an anaerob zone within thematerial. A number of aspects of the invention are not described by thisreference. This applies, among other things, to the pre-treatment suchas the alkaline hydrolysis, welfare in the animal houses, stripping ofammonia before biogas production, prevention of struvite formation etc.and the use of biogas through a local gas engine or through anestablished pipeline for natural gas.

U.S. Pat. No. 6,171,499 describes an improved method to fermentatedomestic and industrial waste. The waste is anaerob digested withproduction of biogas, which is utilized in a gas turbine in combinationwith natural gas. The fermented material is dehydrated and the sludge isdiverted to a incineration plant A number of aspects of the inventionare not described by this reference. This applies, among other things,to the pretreatment such as the alkaline hydrolysis, welfare in theanimal houses, stripping of ammonia before biogas production, preventionof struvite formation etc. and the use of biogas through a local gasengine or through an established pipeline for natural gas.

WO8400038 describes the production of biogas and degassed and stabilisedfertilisers. The thermofil degradation occurs in an inner reactor andthe mesofil degradation in an outer reactor. A number of aspects of theinvention are not described by this reference. This applies, among otherthings, to the pre-treatnent such as the alkaline hydrolysis, welfare inthe animal houses, stripping of ammonia before biogas production,prevention of struvite formation etc. and the use of biogas through alocal gas engine or through an established pipeline for natural gas.

WO8900548 describes the utilization of Ca-ions and Mg-ions in the biogasproduction. The metal ions inhibit foam production. A number of aspectsof the invention are not described by this reference. This applies,among other things, to the pretreatment such as the alkaline hydrolysis,welfare in the animal houses, stripping of ammonia before biogasproduction, prevention of struvite formation etc. and the use of biogasthrough a local gas engine or through an established pipeline fornatural gas.

WO9102582 describes a plant and a method to produce gas and avoidspreading of harmfull compounds to the surroundings by washing the gas.A number of aspects of the invention are not described by thisreference. This applies, among other things, to the pre-treatment suchas the alkaline hydrolysis, welfare in the animal houses, stripping ofammonia before biogas production, prevention of struvite formation etc.and the use of biogas through a local gas engine or through anestablished pipeline for natural gas.

WO9942423 describes a method and a plant to the production of biogas.Fibres and particles from manure is composted and the liquid fraction isfermented anaerobically, stripped for nitrogen. The salts of P and K isutilised for fertilisers by reverse osmosis. A number of aspects of theinvention are not described by this reference. This applies, among otherthings, to the pre-treatment such as the alkaline hydrolysis, welfare inthe animal houses, stripping of ammonia before biogas production,prevention of struvite formation etc. and the use of biogas through alocal gas engine or through an established pipeline for natural gas.

www.igb.fhg.de/Uwbio/en/Manure.en.html describes a process to producebiogas from manure. From degassed manure the solid fraction is used toproduce compost. From the liquid fraction is nitrogen collected and isused as fertilisers. A decanter centrifuge can be used to separate solidcomponents from the mixture. A number of aspects of the invention arenot described by this reference. This applies, among other things, tothe pre-treatment such as the alkaline hydrolysis, welfare in the animalhouses, stripping of ammonia before biogas production, prevention ofstruvite formation etc. and the use of biogas through a local gas engineor through an established pipeline for natural gas.

rieera.ceeeta.pt/images/ukibo_mass.htm describes a production of biogasby anaerob degradation. A decanter centrifuge can be used in the system.A number of aspects of the invention are not described by thisreference. This applies, among other things, to the pre-treatment suchas the alkaline hydrolysis, welfare in the animal houses, stripping ofammonia before biogas production, prevention of struvite formation etc.and the use of biogas through a local gas engine or through anestablished pipeline for natural gas.

www.biogas.ch/f+e/memen.htm describes possibilities to reduce a mixturefrom solid components. Rotating disc reactor, fixed film reactor,ultrafiltration and reverse osmose is mentioned. A number of aspects ofthe invention are not described by this reference. This applies, amongother things, to the pre-treatment such as the alkaline hydrolysis,welfare in the animal houses, stripping of ammonia before biogasproduction, prevention of struvite formation etc. and the use of biogasthrough a local gas engine or through an established pipeline fornatural gas.

www.biogas.ch(f+e/grasbasi.htm describes anaerob degradation of silageenergi crops and manure with the production of biogas. Two processes isdescribed: 1. Silage energi crops is cut into 1-3 cm and directed to aliquid fraction containing the manure. The mixture i fermented at 35° C.2. A dry fermentation of manure and silage energy crops without addingfurther liquid. A number of aspects of the invention are not describedby this reference. This applies, among other things, to the pretreatmentsuch as the alkaline hydrolysis, welfare in the animal houses, strippingof ammonia before biogas production, prevention of struvite formationetc. and the use of biogas through a local gas engine or through anestablished pipeline for natural gas.

www.biogas.ch/f+e/2stede.htm describes the production of biogas. Theorganic waste is hydrolysed and acidified in a rotating sieve-drum fromwhich the liquid fraction continuos is directed to anaerob degradationof with the production of biogas. A number of aspects of the inventionare not described by this reference. This applies, among other things,to the pre-treatment such as the alkaline hydrolysis, welfare in theanimal houses, stripping of ammonia before biogas production, preventionof stuvite formation etc. and the use of biogas through a local gasengine or through an established pipeline for natural gas.

SUMMARY OF THE INVENTION

The present invention shall demonstrate a new way of utilizing energycrops, namely through anaerobic co-digestion in farm scale biogas plantswith animal manures. The process also includes slurry separation, i.e.,refinement of nutrients in the animal manures.

The invention can also be used to co-digest animal cadavers, meat andbone meal etc. with animal manures/energy crops and thus to provide away of disposing off animal cadavers etc. while at the same timefacilitate the production of fertilizers produced from the input of theanimal wastes along with the crops, manures etc.

The process design makes it possible to use annual fodder crops such asbeets, maize or clover grass, all crops with a higher dry matter yieldper hectare than grain cereals. The fodder crops are also beneficial as“green crops” and in crop rotations. The energy potential when using theset aside land for energy crop production shall thus be demonstrated bythe present concept.

The central and obvious vision—under a wide variety of circumstances—isthat the biogas production based on this concept shall in the future becompetitive compared to the use of natural gas and thus be commercialattractive and preferably not subsidised. It is also the vision that theenergy production shall constitute a substantial part of the Danishenergy consumption, i.e. of the same order of magnitude of the use ofnatural gas (about 150 PJ annually). In addition to this effect are thebenefits in terms of environment, animal welfare and food safety.

Parsby has estimated an energy potential when using energy crops, inparticular grain cereals, to 50-80 PJ annually. In the short run thisrequires an area of 150.000 ha and in the longer run an area of 300.000ha. However, based on an dry matter yield of 15 tons per ha in beetsincluding tops to be digested in biogas plants the energy potentialbecomes about 100 PJ annually. The energy from the co-digested manuresshall be added to this (about 25 PJ). With the new cultivars of beetsthe yields of dry matter may substantially exceed the present levels,i.e., yields of the order of 25 tons per hectare.

The core of the invention is a combination of processes which allowsincreased biogas production, stripping of ammonia and a subsequentoptional further use and processing of the digested and stripped remains(the reject water).

It is characteristic that the core of the invention allows furthersimple and robust processes to be integrated with the core of theinvention. A simple and robust energy plant with outstanding energy andeconomic performances as compared to conventional plants is achieved.The energy plant is further integrated with the management of the animalholdings and the agricultural land. Hence a number of aspects constitutethe invention.

In a first preferred aspect the invention may be applied to combatinfections and spread of animal microbial and parasitic pathogens suchas Campylobacter, Salmonella, Yersinia, Acaris and similar microbial andparasitic organisms to air and agricultural land. The threat to humansof being infected is thus reduced if not eliminated.

In a second preferred aspect the invention may be applied to reduce BSEprions contained in manures, fodder, slaughterhouse waste, flesh andbone meal etc. This is achieved by a combination of pre-treatment anddigestion. As part of this aspect, the present invention provides onepossibility for handling animal cadavers, slaughter house waste etc.which enables the exploitation of the nutrients contained in the animalcadavers as fertilizers. The reduction and/or elimination of BSE prionscontained in animal cadavers, meat and bone meal etc. but also manures,fodder, slaughterhouse waste, etc. during the process of the inventionis a prerequisite for this way of handling the waste This is achievedaccording to the invention by a combination of pre-treatment anddigestion. This procedure is an alternative to the present procedure(however now presently prohibited by the EU commission) of processinganimal carcasses in central plants and producing various products suchas meat and bone meal to be used mainly as animal feed.

In a third preferred aspect the invention may be applied to separate themain nutrients nitrogen (N) and phosphorus (P) from animal manures andrefine the nutrients to fertilizer products of commercial quality.

In a fourth preferred aspect the invention may be applied to producelarge amounts of biogas from a wide range of organic substratesincluding all types of animal manures, energy crops, crops residues andother organic wastes.

In a fifth preferred aspect the invention may be applied to ensureoptimal animal welfare and health when stabled in the animal houseswhile at the same time reducing emissions of dust and gasses such asammonia. This is achieved by flushing or re-circulating reject waterthrough the animal houses.

In a sixth preferred aspect the invention may be applied to benefit fromthe full range of advantages associated with the various aspects of theinvention.

In further preferred aspects any combination of the core invention withany one or more of the other aspects mentioned may be preferred.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 discloses one preferred embodiment of the present invention. Inthis embodiment, manure, preferably in the form of a slurry, generatedin a house or stable (1) for the rearing of animals, including domesticanimals, such as pigs, cattle, horses, goats, sheep; and/or poultry,including chickens, turkeys, ducks, geese, and the like, is transferredto either one or both of a first pretreatment tank (2) and/or a secondpretreatment tank (3).

The working principles are that the manure, preferably in the form of aslurry including, in one embodiment, water such as reject water used forcleaning the house or stable, is diverted to the first pretreatment tankcomprising a stripper tank, where ammonia is stripped by means ofaddition to the stripper tank of e.g. CaO and/or Ca(OH)₂. However,addition of CaO and/or Ca(OH)₂ to the slurry may also take place priorto the entry of the slurry into the first treatment tank or strippertank.

At the same time as the addition of CaO and/or Ca(OH)₂, or at a laterstage, the pretreatment tank comprising the stripper tank is subjectedto stripping and/or heating, and the stripped N or ammonia is preferablyabsorbed prior to being stored in a separate tank (11). The stripped Nincluding ammonia is preferably absorbed to a column in the strippertank comprised in the first treatment tank before being directed to theseparate tank for storage.

Organic materials difficult to digest by microbial organisms duringanaerobic fermentation are preferably pretreated in a secondpretreatment tank (3) prior to being directed to the first pretreatmenttank (2) comprising the stripper tank as described herein above. Suchorganic materials typically comprise a significant amounts of e.g.cellulose and/or hemicellulose and/or lignin, e.g. preferably more than50% (w/w) cellulose and/or hemicellulose and/or lignin per dry weightorganic material, such as straws, crops, including corn, crop wastes,and other solid, organic materials. N including ammonia is subsequentlystripped from the pretreated organic material.

In both the first and the second pretreatment tank, the slurry issubjected to a thermal and alkali hydrolysis. However, the temperatureand/or the pressure is significantly higher in the second pretreatmenttank, which is therefore preferably designed as a closed system capableof sustaining high pressures.

Finally, the slurry having been subjected to a pre-treatment asdescribed herein above is preferably diverted to at least onethermophile reactor (6) and/or at least one mesophile biogas reactor(6). The slurry is subsequently digested anaerobically in the reactorsconcomitantly with the production of biogas, i.e. gas consisting ofmainly methane optionally comprising a smaller fraction of carbondioxide. The biogas reactor(s) preferably forms part of an energy plantfor improved production of energy from the organic material substrate.

The biogas can be diverted to a gas engine, and the energy generatedfrom this engine can be used to heat the stripper tank. However, thebiogas can also be diverted into a commercial biogas pipeline systemsupplying household and industrial customers.

The remains from the anaerobic fermentation, still in the form of aslurry comprising solids and liquids, is preferably diverted, in apreferred embodiment, to at feast decanter centrifuge (7) for separatingsolids and fluids. One result of this separation is an at leastsemi-solid fraction comprising almost exclusively P (phosphor), such asan at least semi-solid fraction preferably comprising more than 50%(w/w) P (12). In the same step (7), or in another decanter centrifugeseparation step (8), an at least semi-solid fraction preferablycomprising almost exclusively K (potassium), such an at least semi-solidfraction preferably comprising more than 50% (w/w) K (13) is preferablyalso obtained. These fractions, preferably in the form of granulatesobtained after a drying step, including a spray drying step or a slurrydrying step, preferably comprise P and/or K in commercially acceptablepurities readily usable for commercial fertilisers (10). Suchfertilisers may be spread onto crops or agricultural fields. The liquids(9) also resulting from the decanter centrifuge separation step, such asreject water, can also be diverted to agricultural fields, they can bediverted back to the stable or animal house, or into a sewage treatmentsystem.

In a further embodiment, the first pretreatment tank may be suppliedwith organic material originating from silage tanks (4) comprisingfermentable organic materials. The divertion of such organic materialsto the first pretreatment tank may comprise a step involving an anerobicfermentation such as e.g. thermophilic fermentation tank capable ofremoving gasses from the silage. Additionally, straws and e.g. cropwastes originating from agricultural fields (5) may also be diverted tostables or animal houses and later to the first and/or secondpretreatment tank.

FIG. 2 illustrates an embodiment essentially as described in FIG. 1, butwith the difference that only phosphor (P) is collected followingdecanter centrifuge separation, and water in the form of reject water iscollected in a separate tank for further purification, including furtherremoval of N, removal of odours, and the majority of the remainingsolids. This may be done e.g. by aerobic fermentation. Potassium (K) mayalso be separated from the liquids at this stage.

FIG. 3 illustrates an embodiment comprising a simplified approach to thecombined biogas and slurry separation system according to the presentinvention. In this embodiment, no biogas fermentors are used, and thesolids resulting from pretreatment in pretreatment tanks one (2) and/ortwo (3) are subjected to decanter centrifuge separation (4 and 5)following stripping of N including ammonia and collection thereof in aseparate tank (8). Separate and at least semi-solid fractions comprisingP and K are obtained (9 and 10).

FIG. 4 illustrates an embodiment wherein the potassium (K) is notseparated following decanter centrifuge separation as described for theembodiment illustrated in FIG. 3. Further separation of K from thereject water subsequently collected is however possible.

FIGS. 5 and 6 illustrate a preferred embodiment of the system accordingto the invention. The individual components are described herein indetail.

Further preferred embodiments of the present invention are described infurther detail herein below.

DETAILED DESCRIPTION OF THE INVENTION

The present invention pertains to a number of individual aspects asdescribed herein further below.

The First Aspect (Sanitation)

The first aspect includes a system consisting of a first device, a houseor stable for the rearing of animals including domestic animals such aspigs and cattle, and/or a second device mainly for stripping of ammoniaand pre-treatment of the substrate and/or a third device mainly anenergy plant for improved production of energy from the substrate.

The system can preferably consist of an animal house and a stripper tankand a biogas reactor. Additional components can include a device foraddition of CaO or Ca(OH)₂ to the slurry, an absorption column operatedon the basis of e.g. sulphuric acid, a storage tank for the ammoniaconcentrate, and a storage tank for digested slurry.

The produced biogas can desirably be used for production of current andheat in a gas motor and generator, the current preferably being sold toa net and the heat preferably used for heating of e.g. slurry and/oranimal houses. The energy plant according to the invention has anoutstanding performance in terms of the energy production per unitsubstrate treated in the plant. The outstanding performance is achievedby a combination of pre-treatment of the substrate to be digested,whether animal manures or other organic substrates, with stripping ofammonia from the substrate before anaerobic digestion.

The advantages associated with the present invention are described inmore detail herein below. One central aspect of the sanitation aspect ofthe invention is a pretreatment comprising—alone or in combination—anumber of individual pretreatment steps described in detail in thefollowing:

Pre-treatment of slurry following removal from the animal houses caninclude any one or more of the following steps: 1) ammonia stripping, 2)hydrolyses of organic matter, 3) sanitation of the slurry, 4) reductionof foam formation, 5) flocculation, 6) precipitation of P, and 7)prevention of struvite formation.

The working principles are that slurry is diverted from the first deviceto a stripper tank where ammonia is stripped by means of addition of CaOor Ca(OH)₂, stripping and heat and absorbed in a column before stored ina tank. At the same time the slurry is subject to a thermal and alkalihydrolysis, preferably by using a lime cooker. Finally the pre-treatedslurry is diverted to the third device, consisting of one or twothermopile/mesopile biogas reactors, where the slurry is digestedanaerobically under the production of biogas, i.e. gas consisting ofmainly methane with a smaller fraction of carbon dioxide. The biogas isdiverted to a gas engine and the heat from this engine is used to heatthe stripper tank. The current produced is sold to the net.

As straw and possibly also sawdust is a significant fraction of deeplitter from cattle and poultry holdings, there is a need for a specificpre-treatment of these manures before optimal use as substrate formethane production in biogas plants. Lime pressure cooking representsone preferred pre-treatment method in this respect. Deep litter treatedby this technology can thus be made available for methane production ina more efficient way and result in an increased biogas production.Additionally, it is assured that uric acid and urea dissociates toammonia and that proteins and other substances are dissolved. It ishereby ensured that the inorganic nitrogen from the deep litter can becollected in the N-concentrate by the ammonia stripping process.

The availability of the N in the deep litter and poultry manure toagricultural crops is therefore substantially increased. It is estimatedthat the potential utilization efficiency can be increased to about 90%as is the case for the other manures treated in the biogas and slurryseparation plant according to the present invention.

Alternatively, it may be appropriate to digest the poultry manure in thefirst thermo- or mesopile reactor before passing it to the strippertank. This depends on the quality of the manure and to which degree theuric acid dissociates due to the two different treatments. Experiencegained after some working time of the plant shall clarify this. It isimportant to stress the versatility of the plant which allows all typesof manure and energy crops to be treated.

The technical construction is relatively simple because a screw conveyorequipped with a macerator, all made of rust- and acid proof steel,conveys the biomass into a lime cooker where the mass is heated by asteam injection to 180-200° C. The pressure becomes 10-16 bar during the5-10 minutes necessary for the mass to be treated.

The unit to be constructed shall be able to produce temperatures andpressures in the temperature interval of 100-200° C. Hereby it ispossible to adjust the treatment to different biomasses to be digestedin the plant according to the invention under due consideration to useof energy, tar formation and technical parameters.

Foam formation represents a common problem in biogas plants. Onepreferred choice for controlling foam formation in biogas plants, inparticular when supplied with large amounts of biomass from e.g. energycrops, is rape oil, which in addition to the effect of foam control alsois a substrate for methane gas formation. Ca-ions are also veryefficient in controlling foam as are many salts. One preferred foamcontrolling measure of the present invention is Ca(OH)₂ and/or CaO inaddition to its other effects mentioned earlier. Supplementing theslurry with Ca-ions is also believed to stimulate the formation offlocks and the bacterial adhesion to organic particles and thus theperformance of the anaerobic digestion.

Accordingly, if additional foam control and/or flocculation is needed inthe process because of a very high gas production the fermenters may besupplied directly with Ca and/or rape oil. The addition of Ca(OH)₂ orCaO will also lead to precipitation of bicarbonates as CaCO₃. Thisreduces the CO₂ concentration in solution and in the gas phase andcontribute to the reduction of foam formation through reduced carbondioxide emissions.

Addition of Ca(OH)₂ or CaO in connection with stripping of ammonia andsanitation of the slurry will also lead to precipitation oforthophosphate, i.e. dissolved P(PO₄ ⁻). These P-particles may besuspended in the slurry as well as other flocks. The use of Ca will alsolead to a limited reduction of chemical oxygen demand (COD), which meansthat Ca precipitates other salts than just the orthophosphate.

It is believed that—irrespective of the chemical differences betweenvarious organic waste products, a simple heat treatment and inparticular heat treatment in combination with alkali hydrolysis willlead to an increased gas yield. Furthermore, a combination of hightemperatures and high pH during pre-treatment is believed to result in amore effective sanitation of the organic material as compared toanaerobic digestion alone, whether thermofile or mesofile.

It should be noted that in the Statutory Order no. 823 from the Danish.Ministry of Environment and Energy, it is laid down that a controlledsanitation consists of 1 hour residence time at 70° C. In view thereof,a treatment according to preferred embodiments of the inventionconsisting of one week residence time at 70° C. before two subsequentanaerobic digestions (thermo- or mesofilic) is believed to completelyeliminate all known veterinary and/or human microbial and zoonoticpathogens. Preferably, BSE prions are also eliminated or at leastsignificantly reduced in number.

The overall result is that all infectious organisms in the slurry areeliminated and therefore not spread to the environment when the manureis applied to land. This also makes it possible to flush the firstdevice (the animal houses) with the digested slurry in order to maintainthe sties etc. clean. Cross infections among animals are thus prevented.It also allows further use of water to rinse animals and sties, airexhausts etc. with the effects of preventing emissions to air of odour,dust and infectious agents. This is possible because the slurry withadditional water shall not be stored till periods where land speeding ispermitted. The slurry without N may be spread to land throughout theyear.

However, in the first aspect it is the pre-treatment and thus thesterilization of the slurry which is preferred in order to to allowsubsequent spreading onto agricultural fields.

It will be clear that the present invention relates to a variety ofdifferent aspects, which constitute, individually or in combination,patentable inventions in their own right. The below section contains adescription of various individual parts (components) of one aspect ofthe present invention. An overview of the components are given in FIGS.5 and 6.

It will be understood that selected components can form the basis forother aspects of the present invention. The invention shall in no way belimited to the combination of the entire list of components describedherein below. It will be clear from the description when other aspectsof the invention are related to only some of the components describedherein below. Non-limiting examples of such aspects includes devices forconcentration of N (nitrogen) and/or P (phosphor) and/or K (potassium);energy generation based on the components of stripper tank, lime cookerand fermentor; and animal welfare/reject water processing.

It will also be understood that the below aspects related—among otherthings—to the aspect of sanitation, does not necessarily have tocomprise all of the components illustrated below. Aspects related tosanitation are also understood to comprise a combination of only some ofthe components described herein below.

Animal Houses

The animal houses (Component number 1) serves to provide an optimal foodsafety and food quality, an optimal animal welfare and workingconditions for the labour personal in the housings, an optimal slurrymanagement, suitable for treatment in the GreenFarmEnergy plant, and areduction of emissions to the external environment to a minimum(ammonia, dust, odour, methane, dinitrogen oxide and other gasses).

The housing system can consist of one or more early weaning houses witha total of 10 sections designed to produce 250 livestock units annually.Each section houses e.g. 640 piglets (7-30 kg) or 320 slaughter pigs(30-98 kg).

An amount of about 10.000 m3 slurry can be expected to be producedannually. In addition to this volume an amount of 5-10.000 m3 processwater shall be recycled through the houses. The following mainconditions shall preferably be met by the housing system:

1) Two-climate system: The sties shall preferably be designed astwo-climate systems. The back end of the sties shall be equipped with anadjustable coverage providing an opportunity for the pigs to choosebetween a relatively warm environment under the covering and arelatively cold environment in the rest of the sty. The temperaturedifference shall be in the range of 5-10 deg. C.

When the piglets have grown to around 30 kg the coverage shall be usedto allow for generally colder temperatures in the animal house as such.The pigs may keep warn under the coverage. By allowing for coldertemperatures it is possible to increase ventilation also during colderambient periods.

2) Occupation: The pigs are preferably offered straw from an automate.The searching and digging behaviour is hereby stimulated, because theyshall pick out the straw from the automate by themselves. The strawserves also as an energy source in the energy plant.3) Heating: Heat from the energy plant is preferably recyded to theanimal houses. The heat can be provided by two separate circulationsystems. One is located under the covering to 30-35° C., which providesthe pigs with a comfortable micro-climate, keeps the floor dry andreduces bacterial growth on the floor. The second provides heat to theoverall airspace in the house via pipes along the walls of the house.The second circulation is coupled to the ventilation control.4) Showers: Showers are preferably established over the slats. whichcovers ¼ of the total floor area. This motivates the pigs to manure onthe slats. as opposed to the solid floor. The shower water will flushthe manure into the canals preventing malodour, ammonia losses etc. Theclean solid floors substantially reduces the possible infections formpathogens in the manure as Salmonella, Lawsonia etc.5) Flushing: The manure canals are preferably flushed several times aday. It is provided by flushing of canals with process water from theenergy plant. The manure is diverted to a central canal through a valve.6) Canal design: The surface of the manure is reduced by use of V-shapedcanals and an optimal flushing of the canals are achieved at the sametime. This is central for the reduction of emissions from the animalhouses.7) Ventilation: The ventilation is designed so that 20% of the maximumventilation is diverted down under and through the slats. into centralventilation shack. between the double V-canals. In 60-80% of the year20% of the maximum ventilation is sufficient to provide ambleventilation.8) Feeding: Foodstuff is provided by a wet feeding equipment whichprovides fodder ad libitum.Slurry Collection Tank

The function of a slurry collection tank (Component number 2) is tocollect slurry form the daily flushings of the animal houses and to workas a buffer before pumping to the main reception tank. The slurry isdiverted to the collection tank by means of gravitation. The volume canbe anything appropriate, such as e.g. 50 m³. The tank can be made ofconcrete and it can be placed below the floor in the animal houses sothat the slurry form the houses can be diverted to the collection tankbe means of gravitation.

Main Reception Tank

Slurry from the collection tank is preferably pumped to the mainreception tank (Component number 3). Other types of liquid manure/wastemay also be added to the reception tank from other farms/plants. Optionsare mink slurry, cattle slurry, molasses, vinasses, silage etc. This istransported to the reception tank by lorry and is loaded directly intothe reception tank. The volume/capacity is anything appropriate, such ase.g. about 1.000 m³. The level in the stripper tank preferably controlsa pump, which pumps slurry from the reception tank. The dose adjustmentcan be manual or automatic. The maximum capacity can be anythingappropriate under the circumstances.

CaO Addition

When slurry is being pumped from the reception tank 1 to the strippertank, lime is added to the slurry in order to increase the pH. The limeaddition manifold is preferably adjusted to add 30-60 g CaO/kg TS. Thelime is preferably supplied as a powder which can be blown into the silofrom the lorry. The volume/capacity of the silo can be e.g. about 50-75m³. The dose of 30-60 g/kg TS corresponds to app. 6-12 kg CaO per hourwith a slurry capacity of 3.5 m³/h with 6% TS.

When added directly to the slurry (6% TS), the lime dose is about 60g/kg TS yield (about 8.8 kg CaO per hour). It is however preferred toadd the lime directly to the alkali pressure sterilazation andhydrolysis unit. When lime is added directly to the pressure unit (theE-media hold 2G-70% TS), the lime dose is about 30-60 g/kg TS. 60 g 1 kgd.m. equals about 342 kg CaO per batch, while 30 g/kg d.m. equals about171 kg CaO per batch.

Balance Installation

The balance (Component number 5) shall preferably weigh the incomingE-media (energy containing organic material). The suppliers willpreferably specify the type of media which is supplied to the plant,i.e. deep litter, energy crops etc. of various sorts.

The specification shall be made by selecting the relevant E-media on acontrol panel. According to the suppliers panel registration, the weightof received E-media incl. specification of media is recorded.

The control thus specifies for each E-media (see alkali hydrolysis):

-   -   Energy potential    -   The required heating time    -   The required retention time        Reception Station for Deep Litter and Energy Crops

The reception station (Component number 6) shall receive deep litterfrom e.g. poultry or other animals as well as energy crops. The stationis preferably a large silo equipped with several screw conveyors in thefloor. The lorries will empty their load of E-media directly into thesilo. The volume/capacity can be anything appropriate under thecircumstances, such as e.g. a yearly capacity of E-media (about 51.5%TS) of about 9.800 tonnes. The volume of the silo can be from severalcubic meters to about 100 m³, corresponding to three days capacity (65h). The materials are preferably concrete/steel.

Silo for Energy Crops

The silo for energy crops (Component number 7) serves to provide storagemeans for energy crops. The crops are preferably conserved as silage.The volume/capacity can be e.g. from about 5.000-10.000 m⁸. The silo canbe a closed compartment from which silage juice is collected and pumpedto the reception tank.

Transport- and Homogenisation System for Deep Litter and Energy Crops

The transport- and homogenisation system (Component number 8) for deeplitter and energy crops preferably receives E-media from the screwconveyors in the floor of the reception station. The E-media can betransported by additional screw conveyors to the cooking units and atthe same time preferably macerated by an integrated macerator. Thevolume/capacity can be anything required under the circumstancesincluding about 1.5 m3 E.media/hour, or 8.200 tonnes of E-media/year.The capacity of the transport-homogenisation system is preferably notless than about 30 m3/hour. Three fundamental parameters shall controlthe addition of E-media, i.e. volume, weight per volume, and time. Fromthese parameters volume per unit time, time and thus total volume andweight shall be established.

Alkali Pressure Sterilization and Hydrolysis Unit

The alkali pressure sterilization and hydrolysis unit (Component number9) shall serve two main purposes, i.e. firstly elimination of microbialpathogens in the E-media in particular in deep litter from variouspoultry or other animal productions and secondly, at the same timehydrolyse structural components of the litter in order to render themavailable for microbial degradation in the fermentors.

The unit shall also preferably eliminate or at least substantiallyreduce BSE-prions if present in waste introduced into the plant. Suchwaste include flesh- and bone meal, animal fats or similar produce fromthe processing of animals not used for consumption.

Filling of the pressure sterilizer is provided by the transport- andhomogenisation system, which transports E-media into the according totype of E-media as defined on the balance installation.

The pressure cooking unit consists of two identical units, i.e., twoelongated pipe-like horizontal chambers with a central screw. The twopipes are fastned one on top of the other in order to provide for easyloading of the lower pipe. The units are covered by a hollow cape on thedownwards side. The cape shall divert heat to the media from steam underthe cape.

Lime is added to the upper cooking unit from the CaO silo, i.e., 342 kgper batch.

The lower pipe receives pre-heated E-media from the upper unit.

The lower unit is emptied into a small mixertank containing 25 m³. Herethe E-media is mixed with slurry from the reception tank 1, the mixtureis subsequently pumped into the strippertank.

The CaO tupe contains a by pass so that CaO can be added directly intomixing container under the two pipes. The mixing chamber is used formixing sterilized E-media and raw slurry from the reception tank toprovided a homogeneous biomass and to reuse the heat of the E-media.

The central process parameters are dry matter content of the E-media,temperature, pressure and pH. From a wide range of possible combinationsthe optimal parameter setting is a temperature of 160° C., pressure of 6bar, dry matter content og app. 30%, and pH of app. 12.

The retention time in the sterilization unit consists of severalphases: 1. Filling time; 2. Preheating time in the upper pipe; 3.Heating time in the lower pipe; 4. Retention time at the selectedtemperature and pressure; 5. Pressure release time; 6. Emptying time,and 7: CIP time

The filling phase consists of the time required to transport the E-mediainto the pressure sterilizer and mix it with the added slurry. Thefilling time shall be app. 10 min. After filling the E-media shall beheated to 160° C. at 6 bar. Preheating takes place in the upper pipe andfinal heating in the lower pipe. Heating time is expected to be app.30-40 min.

The retention time at the desired temperature and pressure shall be app.40 min (at 160° C. and 6 bar).

Pressure release time app. 10 min. The pressure is released into thestripper tank.

Emptying is achieved by running of the screw conveyors.

CIP time. Cleaning performed on occasion, generally not necessary.

The volume of the pressure cooker is 10 m³ per unit, and the degree offilling is app. 75-90%. The volume of the mixing container is 25 m³.

An example of running conditions are illustrated below.

Range Selected Units TS 10-30 30 % of total weight Temperature 120-160160 ° C. Pressure 2-6 6 Bar PH 10-12 12 pH

At the panel for suppliers where E-media are registrated the followingshall preferably be defined for the control of the sterilization unit:Weight, volume and sort of E-media. It is thus possible to define foreach E-media transported to the pressure cooker the:

-   -   Energy potential for each E-media    -   Necessary heating time    -   Necessary retention time    -   Necessary mixing time with the slurry    -   Necessary energy use depending on E-media    -   Degree of filling, signal from radar/microwave gauge    -   Empirical based values depending on visual monitoring by the        operator        Mixing Tank for Pressure-Sterilized E-media and Raw Slurry

Following sterilization and hydrolysis in the pressure unit, the treatedbiomass is allowed to expand into a mixingtank (Component number 10)preferably located below the pressure unit. Excess pressure (steam) isreleased into the strippertank in order to collect ammonia and transferheat to the stripper tank biomass before expansion into the mixertank.

The purpose of the mixertank is to mix cold raw slurry from thereception tank with hot sterilized E-media in order to obtain heattransfer (re-use of heat) and mixing of the two media.

The volume/capacity is e.g. about 25 m³. Any suitable material can beused, including insulated glasfibre. The working temperature istypically about 70-95° C.

Tank for Liquid Biomass

The liquid biomass contained in the tank for liquid biomass (Componentnumber 11) shall be use to ensure sufficient biogasproduction during thestart up phase of the whole plant. However, it can also be usedoccasionally, when such liquid biomass is available. Liquid biomassinclude e.g. fish oil, and animal or vegetable fats. Vinasses andmolasses can also be used, but this is not preferred because of therelatively high water content and thus low potential energy content perkg product.

The volume/capacity is typically about 50 m³, and a suitable materialfor the tank is stainless steel. The contents of the tank is preferablyliquids and solids having a particle size of max. 5 mm. Stirring as wellas a heating system for temperature control is preferably provided, asare feeding pump(s) to the fermentor(s). The temperature shallpreferably be min. 75° C. so that oily or fatty biomass can be pumpedinto the fermentor(s).

Stripper and Sanitation Tank

The stripper and sanitation tank (Component number 12) preferablyreceives the following media:

-   -   Slurry from reception tank 1 and/or    -   E-media from the pressure cooker, and/or    -   Possibly liquid biomass from biomass liquid tank, and/or    -   Reject water from decanter or possibly after K-separation.

The purpose of the tank is to regenerate heat used in the pressurecooker by heating the slurry from reception tank 1, to mix the E-mediawith slurry and hence to produce a homogeneous feed to the fermentors,to control pH before feeding to fermentors, and to sanitise the slurry.

The stripper and sanitation tank strips ammonia, step I, and the gas isdiverted to an absorption column which is common to the final stripperprocess, step II. Microbial pathogens are eliminated and themedia/slurry is prepared for anaerobic digestion.

One presently preferred shape of the stripper and sanitation tank is:

Bottom/Floor

-   -   With insulated concrete cone, directed downwards angle 20        degrees    -   Impaired stirring/sand is removed from the floor or according to        the mammut pumping system    -   A sand filter is placed in the bottom, which can be emptied        throughout an external pipe connection. It will also be possible        to empty the tank through the filter        Top/Ceiling    -   With cone construction of sandwich insulated Isofatalic        Polyesters (Encapsulated Foam). Cone angle is approximately 10        degrees.    -   Mounted water drizzle system to avoid the production of foam        from the stirring process and the process in common.    -   A slow running stirring system is placed on top of cone to to        ensure the optimal homogenisation,-optmal vaporation of the        ammonia, and optimal distribution of heat in the media.    -   The ammonia is transported through wet air in a pipe to the        absorbing unit        Side/Wall    -   With cylinder construction of sandwich insulated Isofatalic        Polyesters (Encapsulated Foam).    -   Mounted approximately 600 meters of heating 5/4″ pipes in a        cylinder ring shape inside the tank to heat up the media    -   Mounted some temperature transmitters to regulate the heating        process    -   Mounted a pH-measuring instrument to regulate the acid supply to        the media    -   Outside cylinder wall at the bottom is mounted a insulated        valve/pumping room    -   An ammonia steam diffuser is placed in the middle of the tank.        The ammonia steam generated in the alkali sterilisation and        hydrolysing unit is diffused into the media.

Volume/Capacity: The cylinder wall has an inside diameter of about 12 mand a height of 9 m. This means a tank handling volume of approximately1.000 m³ the bottom cone included.

The hydraulic retention time for slurry and E-media is about 7 days, andthe absolute minimum retention time is about 1 hour.

In one preferred embodiment, the bottom is basically made of concrete,arming iron and pressure proof insulation. The surface in contact withmedia is coated with isofatalic Polyester to avoid corrosive damaging ofthe concrete and arming iron. All pipes mounted in the bottom is eitherpolyester or stainless steel. The top and bottom is basically aconstruction of sandwich insulated Isofatalic Polyesters (EncapsulatedSoap). All pipes mounted is either polyester or stainless steel.

Other Components

-   -   The stirring element is made of stainless steel    -   The heating elements is made of coated mild steel and/or        stainless steel    -   All other components placed inside the tank is made of stainless        steel

In one preferred embodiment, default parameter values for stripping ofammonia from slurry in this system are: Temperature of about 70° C.; pHof about 10-12; liquid gas ratio of <1:400, 1 week operation, and morethan 90% affectivity is achieved.

An example of conceivable running conditions are listed below:

Media: All sorts off liquid animal manure and pres- sure sterilizedsolid or liquid E-media, vari- ous liquid organic wastes, CaO. Runningtemperature: 70-80° C. Running gas combination: 80% NH₄, 15% CO₂, 3% O₂,2% other gases Insulation k-value: 0.20 W/m²K Running Max. Pressure: +20mbar abs. (No vacuum) Max. viscosity in media: 15% TS Base/Acid-range:5-10 pH Abrasive rudiments in 1-2% Media (Ex. Sand): Max. temperature inheat- 90 degrees celcius ing elements: Max. effects in heating 600 kWelements: Transmission effect: 7.5 kW/20-25 rpm.

The stripper and sanitation tank supplies the fermentor(s) with treatedmaterial for fermentation. In a timed process the material will betransported to the fermentors. The demand of material depends on thedigestion process in the fermentors. One, two, three or more fermentorscan be employed.

The stripper and sanitation tank is regularly filled with slurry andE-media from the alkali pressure process. Finally, to obtain a drymatter of ˜15% (15% TS). Some level switches regulate the content in thetank. A TS-measuring unit regulates the content of TS. Every 1 hourafter filling of slurry and E-media it is possible to pump E-media tothe fermentor(s).

The top of the stripper and sanitation tank is preferably ventilatedthrough an ammonia-absorbing unit (Step I), and a pH-measuring unitregulates the need for CaO.

The temperature of the E-media is regulated through temperaturetransmitters.

A timed process can optionally pump water/slurry into the drizzle systemto prevent production of foam.

Fermentors for Biogas Production

Digestion of the biomass is provided by a multi-step fermentor systempreferably comprising three fermentors (Components 13, 14 and 15).Systems with fewer as well as more fermentors can also be applied.

The fermentors are preferably connected to achieve maximum flexibilityand optimum biogas production. The fermentors shall be planned forroutinely running at termofile (45-65° C.) as well as mesofile (25-45°C.) temperatures.

The digestion process can be optimised in terms of organic loading rate,retention time, and maximum digestion (min. 90% of VS). Heat spirals areincluded in order to heat the biomass to the preferred runningtemperature.

A top fastened slow running stirrings system ensures optimalhomogenisation and distribution of heat in the biomass.

Regulation of pH is possible through addition of an organic acid(liquid) in necessary quantities.

The fermentors preferably receives the following media:

-   -   E-media from the stripper and sanitation tank    -   Liquid biomass from the liquid biomass tank    -   Acids from the acid tank

The specific shape of the tank can in one preferred embodiment be:

Bottom/Floor

-   -   With insulated concrete cone, directed downwards angle 20        degrees    -   Impaired stirring/sand is removed from the floor or according to        the mammoth pumping system    -   A sand filter is placed in the bottom, which can be emptied        throughout an external pipe connection. It will also be possible        to empty the tank through the filter        Top/Ceiling    -   With cone construction of mild steel. Cone angle is        approximately 10 degrees    -   Mounted water drizzle system to avoid the production of foam        from the stirring process and the process in common    -   A slow running stirring system is placed on top of cone to        ensure the optimal homogenisation, and optimal distribution of        heat in the media.    -   The biogas is transported through wet air in a pipe to the        gasbag.        Side/Wall    -   With cylinder construction of mild steel.    -   Mounted approximately 600 meters of heating 5/4″ pipes in a        cylinder ring shape inside the tank to heat up the media    -   Mounted some temperature transmitters to regulate the heating        process    -   Mounted a pH-measuring instrument to regulate the acid supply to        the media    -   Outside cylinder wall at the bottom is mounted a insulated        valve/pumping room

The volume/capacity of each tank canhave any suitable net volume,including a net volume of about 1.700 m³.

The materials for the fermentors can e.g. be as specified below:

Bottom

-   -   The bottom is basically made of concrete, arming iron and        pressure proof insulation    -   The surface in contact with media is coated with Isofatalic        Polyester to avoid corrosive damaging of the concrete and arming        iron    -   All pipes mounted in the bottom is either polyester or stainless        steel        Top and Wall    -   The top and wall is basically a construction of mild steel    -   All pipes mounted is either polyester, stainless steel or mild        steel        Other Components    -   The stirring element is made of mild steel    -   The heating elements is made of mild steel    -   All other components placed inside the tank is made of stainless        steel or mild steel

The running conditions can be any conditions suitable, including

Media: All sorts off animal manure, primarily pigs slurry. Maceratedenergy crops. Some sorts of organic waste, CaO, organic Acids Runningtemperature: 35-56° C. Running gas combination: 65% CH₄, 33% CO₂, 2%other gases Insulation k-value: 0.25 W/m²K heatloss is estimated to 10kW Running Max. Pressure: +20 mbar abs. (No vacuum) Max. viscosity inmedia: 12% TS Base/Acid-range: 5-10 pH Abrasive rudiments in 1-2% media(Ex. Sand): Max. temperature in heat- 80 degrees celcius ing elements:Max. effects in heating 600 kW elements: Transmission effect: 7.5kW/20-25 rpm

The digestion shall be run at about 55° C. Heat loss is estimated toabout 10 kW. The biomass in the tank is can be heated from 5° C. to 55°C. during 14 days, and the possibility of addition of acid foradjustment of pH.

Tank for Organic Acids for pH Adjustments in Fermentors

A tank for organic acids (Component number 16) for pH adjustments in thefermentor(s) is preferably also provided.

Buffer Tank for Degassed Slurry Before Decanter

Following digestion of the biomass in the fermentors the degassedbiomass is pumped to a small buffer tank (Component number 17) beforebeing subjected to separation in the decanter.

Decanter Installation

The function of the decanter installation (Component number 18) is toextract suspended solids (ss) and P from the biomass.

The decanter separates the digested biomasse into the two fractions i)solids, including P, and ii) reject water.

The solids fraction contains 25-35% d.m. App. 90% of the ss. and 65-80%of the P-content of the digested biomass is extracted. In case ofaddition of PAX (Kemira Danmark) to the buffer tank before separation inthe decanter, app. 95-99% of the P can be extracted. The solids fractionis transported to containers by means of a shaft less screw conveyor.

The rejectwater contains 0-1% ss and dissolved K. The ss depends on theaddition of PAX. The principal component of the reject waters isdissolved K which amounts to app. 90% of the original K-content in thebiomass. The reject water is pumped to the reject water tank.

P-Fraction Transport System and Treatment

From the decanter installation the solid matter fraction (routinelycalled the P-fraction) can be transported to a series of containers bymeans of conveyor screws and belts forming a P-fraction transport system(Component number 19).

A common conveyor band transports P-fraction to a storage where it isstacked into miles, covered with a compost sheet and allowed to compost.The composting process further dries the P-fraction and the d.m.-contentthus increases to 50-60%.

Second N-Stripping Step

Efficient stripping of ammonia from the reject water is preferred, and aresidual level of about 10 mg NH₄—N/ltr or less is preferred.

The second stripping step is preferably carried out by using a steamstripper operated at ambient pressure. The stripper principle benefitsform the different boiling temperatures of ammonia and water. Attemperatures close to 100° C. extraction of ammonia is most efficient.The use of energy in order to heat the feed is an essential runningparameter. The stripper unit shall therefore preheat the feed beforeentering the stripper column to close to 100° C. This is provided by useof steam (or possibly warm water and steam) from the motorgenerator unitin a steam-water heat exchanger.

When heated the feed enters the stripper column and percolates over thecolumn while at the same time being heated to the running temperature bya counter current of free steam. The steam/ammonia gas is subsequentlycondensed in a two step condensator.

From the floor of the column the water now free of ammonia is pumped toa level controlled exit pump.

The stripped ammonia is diverted to the bottom of a two-step scrubbercondensator where the ammonia gas is condensed primarily in a countercurrent of cooled ammonia condensate. The ammonia gas not condensed aresubsequently condensed in a counter current of pure water (possiblypermeate from the final reverse osmosis step). If the use of acid iswanted or necessary it is appropriate to use sulphuric acid at thisstage. It is thus possible to achieve a higher final concentration ofammonia.

The scrubber condensator are preferably constructed from a polymer inorder to allow the use of acids.

Ammonia Absorption Column (for Use With First and/or Second N-Stripping

A condensate scrubber is used in order to gain flexibility concerningaddition of add. The column (Component number 21) is preferablyconstructed in two sections so that the fraction of ammonia notcondensed in the first section is subsequently condensed in the secondsection. This takes place in a full counter current so that addition ofwater is limited as much as possible. Thereby a maximum ammoniaconcentration in the final condensate is reached (larger than 25%). Theammonia product can be pumped out with a separate pump or be taken outfrom a valve on the circulation pump. The absorption may be assisted byaddition of sulfuric acid into the water counter current.

Sulphuric Acid Tank

The sulphuric acid tank is used for storing the sufuric acid used in theN-stripping process. (Component number 22).

NS Tank

The NS tank (Component number 23) is used for storing the stripped N.

Gas Store

It is preferred to establish a gas store (Component number 24) as abufferstore for the feeding of e.g. a motorgenerator engine.

Rejectwater Tank

From the decanter installation the rejectwater is preferably pumped tothe rejectwater tank (Component number 25).

The rejectwater tank is equipped with a submerged micro-filter withstatic operation. The micro-filter shall remove particles larger than0.01-0.1 μm. A negative pressure of 0.2-0.6 bar shall be built up at themembrane. Hence the permeate is sucked through the membrane retainingthe particles on the membrane surface. In order to prevent membranefouling and scaling the coating of the membrane surfaces has to beremoved by a periodic backwash procedure.

A micro-processor control device shall automatically control theextraction of permeate and the backwash procedure. The extraction shallbe interrupted by periodic backwash e.g. for 35 seconds for every 300seconds running time. The total flow shall be 2-6 m3 per h.

Aeration may be applied to assist the micro-filtration. Aeration imposeshear stress on the membrane surface reducing scaling and fouling. Itfurther aerates the rejectwater and stimulates aerobic decomposition ofresidual organic matter, nitrification and denitrification. Possibleremaining odour, nitrate etc. is thus removed during the process ofmicro-filtration.

From this tank the permeate shall be used for:

-   -   Rinsing of the animal houses, canals, slats etc.    -   Further separation. Dissolved K shall be concentrated by means        of reverse osmosis, the K-fraction being stored in a separate        storage tank. Water for rinsing animals houses may also be taken        form this permeate flow.    -   The K may also be concentrated through other means such as        mechanical or steam compression. This depends on the specific        choice for each specific plant and amount of excess heat        available for steam compression.

The reject water tank containing the concentrate from themicro-filtration shall be emptied at regular intervals to remove theparticle concentrate. This shall be added to either the K-fraction orthe P-fraction from the decanter.

K Tank

The K tank (component number 26) serves the purpose of storing thepotassium (K) concentrate.

Gas Cleaning

The biogas produced in the fermentors may contain trace amounts ofhydrogen sulfide (H₂S) which are necessary to remove (Component number27) before burning the biogas in a combined heat and power plant.

The gas shall be cleaned by employing the ability of certain aerobicbacteria to oxidise H₂S into sulfate. The genus shall primarily be thegenus Thiobacillus which is known form several terrestrial and marineenvironments. Other genus may also be used such as Thimicrospira andSulfolobus.

A tank made of glass fiber packed with plastic tubes with a largesurface area shall be rinsed with reject water to maintain the packingmaterial moist. The biogas is diverted through the packed column and anair stream (of atmospheric air) is added to the biogas stream. Theatmospheric air is added to provide an oxygen concentration of 0.2% inthe gas stream, i.e. sufficient to oxidize the H₂S and therefore not toproduce an explosive mixture of biogas and oxygen. A ring side blower isused.

Combined Heat and Power Plant (CHP)

The main component in the CHP (Component number 28) can be e.g. a gasfired engine connected to a generator for production of electric power.The main priority for the CHP is to produce as much electric power aspossible relatively to heat. The engine is preferably cooled by a watercircuit (90° C.) and the heat is used in the plant process and to theheating of e.g. the animal houses.

The exhaust gas is used in a recuperator for steam production. The steamis used as heating source in the plant process, i.e. in the pressuresterilization unit and in the n-stripper unit II (priority one).Depending on the amount of steam it may also be used for concentratingthe K in the rejectwater (seam evaporation).

Between the steam and heat circuit, there will be installed a heatexchanger, so it is possible to transfer heat from the steam system tothe heat system.

In addition to the above mentioned genset there will be installed asteam boiler. This boiler will be used for heat production to start theprocess, and in addition be used as a backup for the genset.

If there is produced more steam than needed in the plant process, therest production can be flashed of in a cooler.

To start the plant process (heating of fermentor tanks) etc., heat isprovided by the oil fired boiler. As soon as gas production is achievedthe oil burner will be switched to a gas burner. As soon as gasproduction is large enough to start the engine, the engine will takeover the heat production.

Potassium Separation

At least two alternatives for separating potassium from the rejectwaterare possible (Component number 29). At relatively high levels ofbiogasproduction the motorgenerator engine produces excess heat (steamat 160° C.) which can be used to concentrate the K. The distillate freeof nutrients may be used for field irrigation or recycled through thewhole plant.

At relatively low rates of biogasproduction a micro-filter can be usedto filter particles larger than 0.01-0.1 ym from the reject waterrendering the permeate suitable for treatment in a standard reverseosmosis filter. The K shall preferably be concentrated to a 10-20%solution.

The Second Aspect (BSE Prions)

In the second preferred aspect the invention may be applied tosubstantially reduce and/or eliminate BSE prions contained in manures,fodder, slaughterhouse waste, flesh and bone meal and the like. This isachieved by a combination of pre-treatment and digestion. Thiscomponents as listed above are supplemented with a device for additionalpre-treatment of the substrate containing BSE prions, e.g. a limepressure cooker. The lime cooking can be used to hydrolyse a variety oforganic substrates including material containing prions.

BSE prions are proteins resistant to protease attack. However, iftreated with lime at temperatures of preferably 140-180° C., pressuresat preferably 4-8 bar, and a pH of about 10-12 the prions are partlyhydrolysed and thus rendered decomposable by microbial enzymes such asproteases, amidases etc. The microbes are present in the bioreactors andbecause the substrate is stripped for ammonia and thus low in total Nversus total carbon the micro organisms are prone to produceadditionally extracellular proteinases and proteases capable ofhydrolysing the BSE prions. The high residence time also contributes toan efficient decomposition of BSE prions.

The Third Aspect (Concentration of N and P)

In a third preferred aspect, the invention may be applied to separatethe main nutrients nitrogen (N) and phosphorus (P) from animal manuresand refine the nutrients to fertilizer products of commercial or“organic” quality. This is achieved by combining the components of thefirst aspect with a decanter centrifuge.

The N and P are the main nutrients in the slurry which are often inexcess in animal holdings. The N is stripped and collected as describedin the first aspect leaving P in the remaining digested slurry. However,if subject to a decanter centrifuge, the P is removed from the slurryalong with organic and inorganic solids.

The result being that preferably more than 90% of the N and P in theslurry are collected in separate fractions. The remaining reject watercontains some potassium (K) and trace amounts of N and P. The rejectwater is thus suitable for land spreading at all times of the year.

It is possible to extract potassium (K) from the reject water by anadditional coupled membrane aeration and filtration. Briefly, ceramicmicro-filters are used as diffusers and filters at the same time. Thefilters are submerged in the reject water and operated with intermittentaeration and filtration periods. Aeration provides decomposition of theremaining organic matter and settling of inorganic flocks. The treatedwater is thus suitable for membrane filtration because fouling andscaling is prevented. Also the aeration through the same membranes (airback flushing) prevents the membranes from fouling and scaling.

The product produced is a concentrate (mainly containing K) and filteredwater suitable for land spreading (a very limited area is required).

As under the first aspect the reject water may also be re-circulatedthrough the animal houses.

The P fraction is suitable to further drying, which produces a granulateof commercial value. The N and K fractions are similarly of commercialvalue.

The third preferred aspect is in particular designed to concentrate themain nutrients N and P (and K) contained in slurry and other organicsubstrates to fertilizer products of commercial quality.

However, if decanter centrifuges are combined with the other elements ofthe GFE biogas and slurry separation system, in particular theN-stripping unit, it becomes of major interest to farmers. Thecombination of the N-stripping and decanter centrifuges means that themajority of the N and P content of the slurry is separated and collectedinto individual fractions. It is important to stress that the P whenpresent in flocks is bound to be stripped by the decanter centrifuge.

They can be used and added to the fields according to the specific needof each nutrient It is also possible to re-circulate the reject watertaken behind the decanter centrifuge through the animal houses. Cleaningof floors and slats in the sties are achieved as is additionaladvantages in terms of good indoor climate, reduced ammonia and othergas emissions, frequent flushing of slurry canals etc.

The reject water may contain a major fraction of the potassium (K),while a smaller part will be present in the P-fraction. This means thatin the scenario where slurry is stripped for ammonia and separated for Pthe N and P can be stored and applied according to specific needs, whilethe reject water can be applied throughout the year as waste water.

It can be estimated that the need of spreading area is about ¼ of thearea required for slurry application, the harmony area, and that this ¼part shall run through the whole harmony area over a 4-year period.

Irrespectively of the possibility of treating the reject water further(see section) some farmers will undoubtedly be more than content withthe N- and P-stripping with just one single reactor for digestion of theslurry. Even the P-stripping by the decanter centrifuge may be omittedbecause the N is concentrated leaving a dilute slurry without N whichmay also be spread onto land a any time of the year, except on frozenland.

It is very satisfying that parts of the total system can be offered tofarmers while others may be content with any combination more suitableto their situations. In any case it is the N-stripping which make theuse of decanter centrifuges interesting to practical farming.

The reject water from the complete process may be subjected to a finaltreatment depending on the market preferences.

Thus, the challenge is to treat the reject water to become suitable formembrane filtration and also larger volume reductions than the 50-60%mentioned. The challenge is also to use well known, cheap and robusttechnologies in a new context.

The solution is the following:

Aeration of slurry is well known and aeration with atmospheric airduring 24 weeks produces an aerobic digestion.

Aeration achieves the following:

First, remaining ammonia is stripped and collected in an absorptioncolumn (possibly the same as the one used during pre-treatment) by aso-called low-temperature stripping of about 20° C. A wider liquid-gasratio is required of about 1:2000 (Liao et al. 1995).

Secondly remaining organic matter and smell components are decomposed(Camarero et al. 1996; Burton et al 1998; Doyle and Noüe 1987; Garraway1982; Ginnivan 1983; Bloun et al. 1988).

Thirdly possible remaining ammonia after stripping will be nitrified tonitrate (Argaman Y. 1984; Gönenc and Harremoës 1985).

This aeration shall be combined with filtration by employing new sewagewaste technology, i.e., a micro-filtration principle combining aerationand filtration over ceramic filters (Bouhabila et al. 1998; Scott et al.1998; Zaloum et al. 1996; Engelhardt et al. 1998). An energy efficientaeration and filtration is achieved in one operation. The aeration isfurther used for cleaning of the ceramic membranes by “air backflushing” (Visvanathan et al 1997; Silva et al 2000).

This leaves a water phase well suited to separation over standardosmosis membranes if necessary, because possible scaling and foulingproblems are minimal. It is therefore hypothesized that a larger volumereduction can be achieved at substantial lower energy costs, althoughsome energy is used for the aeration.

Even if membrane filtration is not used, aeration it self may bemotivated by the final stripping of ammonia and by removal of theremaining smell components.

The Fourth Aspect (Renewable Energy)

The main devices of this preferred aspect are pre-treatment facilitiesconsisting of a stripper tank and a lime cooker, and a flexible andmulti step (minimum 3-step) process design of bioreactors.

In the fourth preferred aspect the invention may be applied to producelarge amounts of biogas from a wide range of organic substratesincluding all types of animal manures, energy crops, crop residues andother organic wastes.

The pretreatment facilities of first and second preferred aspects allowthe use of a variety of organic substrates while the multi-stage biogasplant allows a complete digestion of the substrate and thus a maximumenergy yield.

N-rich and recalcitrant substrates such as poultry manure and deeplitter is pretreated in the lime cooker. The cooked substrate ispre-digested in a mesopile reactor before the substrates enters thestripper tank and the subsequent reactors.

The pre-digestion ensures that the readily available organic matter isdecomposed and the N released into solution as ammonia. The bulk of theN is thus is thus collected in the stripper tank and the recalcitrantorganic substrate being decomposed in the subsequent reactors of theenergy plant. Alternatively, depending on the quality of the substrate,it may enter directly into the stripper tank before digestion in thereactors. The result is that large amounts of biogas is being produced,i.e. typically 5 to 10 times more energy than contained in slurry.

The treatment in the GFE biogas and separation system further ensuresthat the nutrients are re-circulated to agricultural land. The energycrops are digested in a separate reactor and the digested biomass isdiverted to the stripper tank. In this tank the fibres not decomposedduring residence in the separate reactor will be hydrolysed and theammonia will be collected in the N-fraction. The N contained in energycrops can then be re-circulated to land and used in the production ofnew energy crops. About 1-3 kg N per tonnes silage can be reused.

The organic material according to the invention is preferably strippedfor ammonia which in particular at thermopile temperatures is inhibitoryto the biogas process (Hansen et al. 1998; Krylova et al. 1997;Kayhanian 1994). The ammonia is stripped during the pretreatment, wherethe biomass is also being hydrolysed etc.

The process can preferably be split in a thermopile and a mesopilecomponent (Dugba and Zhang 1999; Han et al. 1997; Gosh et al. 1985;Colleran et al. 1983). This gives rise to increased energy yields andworking stability, among other thing because the biomass resides longerin the bioreactors which allows the methane bacteria time decompose thesubstrate. It should be noted that more energy for heating is requiredas is a larger total reactor volume.

In addition to this two-step principle the plant shall make use of yetanother reactor to preliminary digestion of poultry manure and similarN-containing biomasses. Also the energy crops shall be digested in thisreactor before further processing in the energy plant. During this firstdigestion the main fraction of the readily available organic matter isdecomposed and the nitrogen released into solution in the form ofammonia. The nitrogen can now be stripped in the stripper tank andcollected in the N-fraction.

Digested beets, maize, clover grass etc. contain about 1 kg N per tonneswet weight and it is therefore important that this N is collected in theN-fraction. Poultry manure is even more N-rich and may also be digestedin the pre-digester before further digestion in the main biogas plant.

The stripping and hydrolysis ensures that also the recalcitrant fibresare made available to digestion as described under the pre-treatment.The following digestion in the main biogas plant ensures a maximum gasyield.

The Fifth Aspect (Animal Welfare)

In a fifth preferred aspect the invention may be applied to ensureoptimal animal welfare and health when stabled in the animal houseswhile at the same time reducing emissions of dust and gasses such asammonia. This is achieved by flushing or re-circulating reject waterthrough the animal houses with the purpose of cleaning and rinsingsties, floors, slats, manure canals etc. This reduces the emittingsurfaces where odour, ammonia and dust may be released to the in-doorair.

The system further allows the use of straw without increasing theemissions of dust and ammonia. The straw is a substantial welfarecomponent, in particular for pigs but also for other animals. Itprovides the animals with digging and occupational material andstructural fodder.

The reject water taken after the decanter centrifuge treatment (thethird aspect) or possibly behind the first digestion (the first aspect)is well suited as a means to flush the animal housings. The flushingremoves the straw and manure mixtures from the slats.

In further preferred aspects any combination of the core invention withthe other aspects mentioned may be preferred. The first aspect ispreferably included in all combinations.

Accordingly, it will be clear from the above descriptions of preferredaspects and embodiments of the present invention that there is providedherein:

A method for improved biogas production, said method comprising thesteps of

-   i) stripping N including ammonia from organic materials including    manures and slurries thereof, and optionally hydrolysing the organic    material,-   ii) diverting the thus obtained organic material to a biogas    fermentor, and-   iii) obtaining biogas from the fermentation of the organic material.

The above method may further comprise the step of separating the solidsresulting from the biogas fermentation in a separation step involving adecanter centrifuge. Separate fractions of P and/or K, preferably ingranulated form, are obtained from this separation.

The above method in another embodiment comprises the further step ofrecirculating the liquids resulting from the biogas fermentation tostables or animal houses, optionally after a further purification step.

In another preferred embodiment, the step of N including ammoniastripping preferably occurs simultaneously with, or sequentially with,in any order, a step involving a thermal hydrolysis step and/or analkali hydrolysis step, wherein any one or both steps take place at anincreased temperature and/or an increased pressure as described hereinabove.

The above preferred embodiments thus in one embodiment solve theproblems associated with environmental contamination by undesirablemicrobial organisms, including Salmonella Typhimurium DT104, and/orprions associated with BSE that are present in organic materialsincluding manures and slurries thereof.

In another embodiment, the above described preferred embodiments solvethe problems associated with an attaining a sufficiently high hygienicstandard in a stable or an animal house. This is achieved by reducingand/or eliminating undesirable microbial organisms and/or prionsassociated with BSE that are present in organic materials includingmanures and slurries thereof.

In yet another embodiment, the above described preferred embodimentssolve the problems associated with an excessive use of expensive waterresources in a stable or an animal house. This problem is solved byre-using reject water obtained from the decanter centrifuge separationstep used for separating solids and liquids resulting i.e. from eitherpretreatment of organic material and/or N stripping including ammoniastripping and/or anaerobic fermentation leading to biogas formation. Atthe same time, it is possible to reduce and/or eliminate the occurrenceof microbial microorganisms in the reject water by further purificationsteps.

The present invention also provides cheep fertilisers of commerciallyacceptable standards. This is achieved by N-stripping including ammoniastripping and separation of P-containing granulates and K-containinggranulates by means of decanter centrifugation following pretreatment,preferably including thermal and alkali hydrolysis.

In another aspect of the present invention there is provided a methodfor reducing the number of viable microbial organisms and/or BSE prionspresent in an organic material, said method comprising the steps of

-   -   i) providing an organic material comprising solid and/or liquid        parts,    -   ii) reducing, in said organic material, the number of viable        microbial organisms and/or BSE prions by subjecting the organic        material to        -   a) a lime pressure cooking step, and/or        -   b) a step wherein the organic material is heated at a            predetermined temperature and/or subjected to a            predetermined pressure and/or subjected to addition of base            or acid, and/or        -   c) a step resulting in at least partial hydrolysis of the            organic material,        -   wherein said processing steps a), b) and c) can occur            simultaneously, or sequentially in any order, and    -   iii) obtaining a processed organic material comprising at least        a reduced number of viable microbial organisms and/or BSE        prions.

A wide variety of microbial organisms can be eliminated by the methodsof the invention, including microbial organisms selected from animalmicrobial organisms, infectious microbial organisms, and parasiticpathogen microbial organisms, including any combination thereof.Examples include, but is not limited to, bacteria such as Campylobacter,Salmonella, Yersinia, Ascaris, similar microbial and parasiticorganisms, as well as virus, viroids and the like.

The lime cooking step may also serve to sterilize the organic materialin which case no viable microbial organisms survive this step ofprocessing. The lime preferably comprises or essentially consists of CaOor Ca(OH)₂.

Preferably, any BSE prions or other prions present in the organicmaterial are also destroyed or eliminated by the sterilization process.When there is a reduction of microbial organisms and/or prions followingany one of the above-mentioned steps, the reduction be e.g. a 90%reduction, an 80% reduction, a 70% reduction, a 60% reduction, or areduction of preferably at least 50%.

It is preferred in one embodiment to improve the production of biogas bylime pressure cooking the organic material before the organic materialis subjected to a N stripping step. However, the lime pressure cookedorganic material can also be fermented prior to being subjected to a Nstripping step.

When the organic material is of plant origin, it can preferably beensued before being diverting to N stripping. The ensued organicmaterial of plant origin can also be fermented prior to N stripping.Organic material to be ensilaged preferably comprises annual foddercrops such as beets, maize, clover grass, and wherein optionally the topof the plants is included.

Lime pressure cooking of the organic material is preferably performed ata temperature of from about 100° C. to about 250° C., under a pressureof 2-20 bar, with addition of lime sufficient to reach a pH value offrom about 9 to about 12, and with an operation time of from at leastone 1 minute to preferably about less than 60 minutes.

The amount of added lime including CaO is preferably from about 2 toabout 80 g per kg dry matter, such as from about 5 to about 80 g per kgdry matter, such as from about 5 to about 60 g per kg dry matter, suchas from about 10 to about 80 g per kg dry matter, such as from about 15to about 80 g per kg dry matter, such as from about 20 to about 80 g perkg dry matter, such as from about 40 to about 80 g per kg dry matter,such as from about 50 to about 80 g per kg dry matter, such as fromabout 60 to about 80 g per kg dry matter.

An example of operating conditions of the lime pressure cooker is atemperature in the interval of about 120° C. to about 220° C., apressure from about 2 bar to preferably about less than 18 bar, and anoperation time of from at least 1 minute to preferably less than 30minutes.

Another example of working conditions includes a temperature in theinterval of from about 180° C. to about 200° C., wherein the pressure isfrom about 10 bar to preferably less than 16 bar, wherein the pH levelis from about 10 to about 12, and wherein the operation time is fromabout 5 minutes to about 10 minutes.

The above method can be following by a number of additional steps. Inone embodiment, there is provided the further steps of diverting theprocessed organic material to a biogas fermenter, fermenting theprocessed organic material and obtaining a biogas. Another further steprelates to supplementing an external environment, including anagricultural field, with the processed organic material. Thesupplementation of the external environment, including an agriculturalfield, can also be performed by using the residual material resultingfrom the fermentation of the processed organic material.

Another further step is that of stripping nitrogen (N), includingammonia, from said organic material prior to diversion to a biogasfermentor of the organic material. This results in an increased andstable biogas production. This also allows the use of N-rich biomassesto be stripped and subsequently digested in the fermentors. Biogas isproduced from the fermentation of the organic material freed from atleast part of the N, including ammonia.

The stripped nitrogen (N) including ammonia is preferably absorbed in acolumn before optionally being stored in a tank. When being absorbed ina column, the stripped nitrogen (N) including ammonia is preferablyabsorbed in a column comprising water or an acidic solution, preferablysulphuric acid, before optionally being stored in a tank.

In one presently preferred embodiment there is provided a methodcomprising the steps of

-   -   i) eliminating, inactivating and/or reducing in said organic        material the number of viable microbial organisms and/or BSE        prions by subjecting the organic material to        -   a) a lime pressure cooking step, and/or        -   b) a step wherein the organic material is heated at a            predetermined temperature and/or subjected to a            predetermined pressure and/or subjected to addition of base            or acid, and/or        -   c) a step resulting in at least partial hydrolysis of the            organic material,        -   wherein said processing steps a), b) and c) can occur            simultaneously, or sequentially in any order,    -   ii) stripping N, including ammonia, from said processed organic        material,    -   iii) diverting the N stripped organic material to a biogas        fermenter,    -   iv) fermenting the N stripped organic material, and    -   v) obtaining biogas and a fermented organic material at least        having a reduced number of viable microbial organisms and/or BSE        prions.

It is much preferred that essentially no BSE prions are present in theorganic material resulting from the fermentation.

The step of stripping nitrogen (N), including ammonia, is preferablyperformed by initially adding an amount of lime to the organic materialsufficient to increase the pH value to above 9 at a temperature ofpreferably above 40° C., such as a pH value of above 10 at a temperatureof preferably above 40° C., for example a pH value of above 11 at atemperature of preferably above 40° C., such as a pH value of about 12at a temperature of preferably above 40° C.

In preferred embodiments, the temperature is preferably above 50° C.,such as above 55° C., for example above 60° C.

The operation time is in one embodiment from 2 to 15 days, such as from4 to 10 days, for example from 6 to 8 days. An example of one set ofprocess parameters is a pH level of from 8-12, a temperature of from 70°C.-80° C., a liquid to gas ratio of less than 1:400, and an operationtime of about 7 days. The alkaline conditions can be generated by addingany base. However, the pH is preferably increased by adding CaO orCa(OH)₂.

The organic material can comprise solid and/or liquid parts such as e.g.manures and slurries thereof, crop residues, silage crops, animalcarcasses or fractions hereoff, slaughterhouse waste, meat and bonemeal, including any combination thereof. In one embodiment, the organicmaterial comprises a maximum of 50% solid parts, for example a maximumof 40% solid parts; such as a maximum of 30% solid parts, for example amaximum of 20% solid parts. The organic material can also be in a liquidstate and comprise a maximum of 10% solid parts.

The organic material can further comprise straw, fibres or sawdust, andin one embodiment the organic material has a high content of fibres,preferably more than 10% (w/w). The organic material can also have ahigh content of complex carbohydrates comprising cellulose, and/orhemicelluloses and/or lignin, such as preferably more than 10% (w/w).Lime pressure cooking cellulose containing organic material results in adisintegration of cellulose into small organic acids such as formicacid, acetic acid, lactic acid, and the like.

The organic material can also comprise deep litter or manure fromanimals, especially from cattle, pigs and poultry holdings.Additionally, animal organic material can be used, such as e.g. animalcarcasses or fractions hereof, slaugtherhouse waste, meat and bone meal,blood plasma or any such produce originating from animals, risk- andno-risk material with respect to the potential presence of BSE-prions orother prions.

In one embodiment the organic material comprises or essentially consistsof solid parts of less than 10 cm in length, such as solid parts of lessthan 5 cm in length, for example solid parts of less than 1 cm inlength.

The organic material can preferably be macerated before being treated inthe lime pressure cooker, preferably by using a screw conveyor equippedwith a macerator, preferably one made of rust and acid proof steel. Theconveyor conveys the organic material into the lime cooker where theorganic material is preferably heated by steam injection, or by steam ina cape around the lime cooker, or any combination thereof.

The organic material can also comprise proteins or similar organicmolecules comprising elements, including amino acids and combinationsthereof, constituting the BSE prions or other prions, and wherein saidBSE prions or other prions are eliminated or destructed directly orrendered available for destruction by lime pressure cooking and/orsubsequent fermentation, including anaerobic fermentation. The organicmaterial of animal origin preferably has a high amount of nitrogen (N),preferably more than 10%.

The organic material in the form of a liquid slurry can be obtained bythe addition of water and/or water containing a low concentration oforganic material, preferably less than 10% solid parts. The added watercan be recycled water, water containing a low concentration of organicmaterial obtained from the silage plant, and/or water collectedfollowing cleaning of stables and/or cleaning of animals, and/or waterobtained from the fermentation before the N stripping process, and/orwater obtained from one or more biogas producing plants, and/or waterobtained during concentration of P fertilisers, and/or water obtainedduring concentration of K fertilisers, and/or collected rain water.

It is in one embodiment particularly preferred that the water is rejectwater obtained from a biogas producing plant, or reject water obtainedduring concentration of P fertilisers, or water obtained duringconcentration of K fertilisers, or collected rain water.

It is preferred that any or most of the urea and/or uric acid present inthe organic material is converted into to ammonia, wherein the ammoniais optionally collected following absorption to a column as describedelsewhere.

Additional steps besides lime pressure cooking is mesophilic and/orthermophilic fermentation. Accordingly, the organic material which hasbeen treated in the lime pressure cooker can subsequently be divertedinto a plant for mesophilic and/or thermophilic fermentation before orafter the organic material is subjected to N stripping.

Each fermentation is performed by a bacterial population capable ofmesophilic or thermophilic fermentation, respectively. The fermentationis in one embodiment an anaerobic fermentation.

The fermentation is preferably performed at a temperature of from about15° C. to preferably less than about 65° C., such as at a temperature offrom about 25° C. to preferably less than about 55° C., for example at atemperature of from about 35° C. to preferably less than about 45° C.

The fermentation is preferably performed for a period of time from about5 to preferably less than 15 days, such as for a period of time fromabout 7 to preferably less than 10 days.

There is in one embodiment provided a method, wherein the biogasproduction is performed in one or more plants by a microbial organism,preferably a population of bacteria, and involves an anaerobicfermentation of the organic material. The bacteria preferably producemainly methane and a smaller fraction of carbon dioxide when fermentingthe organic material. The biogas production can be performed in one ormore plants, preferably by bacterial anaerobic fermentation of theorganic material.

In one embodiment, the biogas production is performed in two plants byanaerobic bacterial fermentation of the organic material, initially byfermentation with thermophilic bacteria in a first plant, followed bydiverting the thermophilicly fermented organic material to a secondplant, wherein fermentation with mesophilic bacteria takes place.

The thermophilic reaction conditions preferably include a reactiontemperature ranging from 45° C. to 75° C., such as a reactiontemperature ranging from 55° C. to 60° C.

The mesophilic reaction conditions preferably include a reactiontemperature ranging from 20° C. to 45° C., such as a reactiontemperature ranging from 30° C. to 35° C. The thermophilic reaction aswell as the mesophilic reaction is preferably performed for about 5 to15 days, such as for about 7 to 10 days.

Any potential foam formation can be reduced and/or eliminated by theaddition of polymers, and/or plant oils, and/or one or more salts,preferably plant oil in the form of rape oil. The salts preferablycomprise or essentially consist of CaO and/or Ca(OH)₂.

A desirable flocculation of substances and particles during biogasproduction is preferably achieved by the addition of calcium-ionscapable of forming calcium-bridges between organic and inorganicsubstances in solution or suspension, wherein said calcium-bridgesresulting in the formation of ‘flocks’ of particles. The addition ofcalcium-ions further results in the precipitation of orthophosphates,including dissolved (PO₄ ³⁻), which is preferably precipitated ascalcium phosphate Ca₃(PO₄)₂, wherein the precipitated calcium phosphatepreferably remains suspended in a slurry.

The obtained biogas can be diverted to a gas engine capable of producingheat and/or electricity. The heat can be used to heat the lime pressurecooker and/or the fermentation plant and/or the N stripper reactorand/or the one or more biogas plant(s) and/or the animal house(s) and/ora human residence and/or heating water to be used in a household orhuman residence. The electricity can be diverted and sold to acommercial net for distributing electricity. In one preferredembodiment, the remaining N stripped, sterilised and fermented organicmaterial is spread on agricultural fields.

In addition to i) reducing and/or eliminating undesirable microbialorganisms, ii) improving the production of biogas, and iii) providing ahighly usable N stripped, sterilised and fermented organic material, theinvention in another aspect pertains to a method for producing Ncomprising fertilisers from organic materials comprising a N source,said production comprising the steps of i) collecting N includingammonia stripped from the organic material in an N stripping step, ii)absorbing said N including ammonia in water or an acidic solutionpreferably comprising sulphuric acid, and iii) obtaining N-fertiliserwhich can be spread on agricultural land.

The invention in yet another aspect provides a method for producingphosphor (P) comprising fertilisers from organic materials comprising aP source, said production comprising the steps of i) diverting slurryfrom a biogas fermenter to a separator, ii) separating the fermentedorganic material as well as inorganic material into a solid and a mainlyliquid fraction, iii) obtaining a mainly solid fraction comprising apart of the P, preferably in the form of calcium phosphate Ca₃(PO₄)₂,and organic phosphates suspended in the slurry, wherein said solidfraction is capable of being used as a P fertiliser capable of beingspread on agricultural land when appropriate.

The separator for separating the fermented organic material as well asinorganic material into a solid and a mainly liquid fraction ispreferably a decanter centrifuge. The mainly solid fraction comprising Pcan optionally be dried to produce a granulate comprising a Pfertiliser, e.g. by allowing the P-fraction to compost in a mile storeunder an air permeable sheet or cover.

The reject water obtained from the biogas production and the separationfrom solid components can preferably be re-used in the fermentation ofsilage and/or in the lime pressure cooking process and/or in the Nstripping process and/or in the biogas plant and/or in cleaning of thestable and/or is spread on land and/or is lead to a conventional sewagetreatment plant.

Accordingly, the method in another aspect provides for the production ofsubstantially clean reject water, said production comprising the stepsof i) obtaining from the separator, preferably a decanter centrifuge, aliquid fraction comprising reject water having only a very limitedcontent of N and P, preferably less than 5% (w/v), such as less than 1%(w/v), for example less than 0.1% (w/v), such as less than 0.01% (w/v),and essentially no sources capable of spreading zoonoses, veterinaryvira, infectious bacteria, parasites or other infectious agents,including BSE prions and other prions. For some embodiments it isacceptable if the reject water contains less than 10% of the N and Poriginally obtained in the slurry.

In another aspect of the present invention there is provided a methodfor producing potassium (K) comprising fertilisers from organicmaterials comprising a K source, said production comprising i) divertingthe liquid fraction from the first separation step (used in theseparation of P containing organic materials as described herein above)to a second separation step, ii) separating the remaining organic andinorganic composition from the liquid, iii) obtaining a solid fractioncomprising K, wherein said solid fraction is capable of being used as aK fertiliser capable of being spread on agricultural land whenappropriate.

The second separation step preferably comprises subjecting the Kcomprising fraction through a ceramic micro filter operating with anintermittent aeration and filtration of the reject water, whereinpreferably said aeration provides decomposition of the remaining organicmaterial and settling of inorganic flocks.

In another aspect there is provided a method for producing clean rejectwater, wherein the obtained reject water is treated in an aerobictreatment system capable of eliminating and/or reducing the content of Nand P within the water and preferably also decomposing the remainingorganic material and smell components, obtaining reject wateressentially free from N and P, wherein said reject water is preferablycapable of being spread on agricultural land when appropriate, orre-circulated through an animal houses.

The above-mentioned aeration can be performed with atmospheric airduring 2-4 weeks at a temperature of about 20° C. and a liquid-gas ratioof about 1:2000. Any eliminated N can be collected and diverted to theabsorption column described herein elsewhere.

By being able to clean animal houses with the reject water treated inthis way, the invention also provides in yet another aspect a method forimproving the hygiene in an animal house or a stable for animals, saidimprovement consisting in cleaning the stable with the obtained rejectwater. The cleaning involves cleaning and rinsing e.g. sties, floors,slats, manure canals, ceilings, ventilation canals, scrubbing exhaustair, etc., as well as reducing the emitting surfaces where odour,ammonia and dust may be released into the environment of thepredetermined location including the stable.

The cleaning of the stables is in one embodiment preferably performedwith reject water obtained following fermentation of energy crops orobtained following the fermentation to produce biogas separation ofsolids and liquids or reject water obtained from a later process in thesystem.

It is also possible according to this aspect of the invention to improveanimal welfare in a stable by utilising straw in the stable as itprovides the animals with digging and occupational material andstructural fodder. It is preferred in one embodiment to divert the strawcomprising organic material from the stable to the lime pressure cookerand hydrolyse the organic material before further processing. Anotheroverall objective of the improvement of animal welfare in a stableresides in the possibility of being able to spray the animals in orderto reduce the number of microbial organisms as well as dust in the fursof the animals and simultaneously reduce the temperature of the animals.

In this way, there is provided a method integrating anaerobicfermentation of animal manures, energy crops and similar organicsubstrates, as well as refinement of nutrients held in the digestedbiomass to fertilizers of commercial quality, in combination withobtaining clean reject water.

The integrated method described herein above requires a system ofcomponents, or a selection of such components, as described herein inmore detail elsewhere.

In one aspect, the system comprises

-   -   i) a first device, preferably animal houses or stables for        holding and/or breeding animals, preferably farm animals        including cows, pigs, cattle, horses, goats, sheep and/or        poultry, and the like, and/or    -   ii) a second device, preferably at least one pre-treatment plant        for pretreatment of organic material, said organic material        preferably comprises animal manure and/or animal slurry and/or        plant parts, wherein said plant parts preferably comprise one or        more of straw, crops, crop residues, silage, energy crops, and        optionally animal carcasses or fractions hereof, slaugtherhouse        waste, meat and bone meal, blood plasma or any such produce        originating from animals, risk- and no-risk material with        respect to the potential presence of BSE-prions or other prions,        and/or    -   iii) a third device, preferably an energy plant generating an        improved amount of energy from a biomass comprising organic        material,    -   in which the first device comprises    -   a) a system for cleaning one or more of floors, slats, sties,        manure canals, slurry canals, animals, and ventilation canals of        an animal house or a stable, said cleaning involving the use of        cleaning water, and/or    -   b) a system to transport the cleaning water, optionally in the        form of a slurry comprising cleaning water and organic material,        from the animal house or stable to the second device,    -   in which the second device comprises    -   a) a first pre-treatment tank, preferably a stripper tank for i)        stripping N (nitrogen), including ammonia, from the slurry        diverted from the first device to the second device, or ii)        stripping N, including ammonia, from organic material diverted        from an additional pretreatment tank of the second devise,        wherein the first pre-treatment tank can optionally also be used        for hydrolysing the organic material, and/or    -   b) a second pre-treatment tank, preferably a lime pressure        cooker for hydrolysing slurry comprising organic material        diverted from the first device to the second device, wherein        said hydrolysis results in eliminating, inactivating and/or        reducing in number any viable microbial organisms and/or        pathogenic substances present in the slurry, or a part thereof,        and/or    -   c) at least one tank, preferably a silage tank for generating        ensued plant material comprising at least one or more of        corn/maize, energy crops, beets, and crop residues, and/or    -   d) at least one second tank, preferably a pretreatment        fermenting tank to ferment silage and/or lime pressure cooked        organic material, in which the fermentation conditions are        selected from mesophilic fermentation conditions and/or        thermophilic fermentation conditions,    -   in which the third device comprises    -   a) at least one biogas fermenter to which slurry and/or organic        material can be diverted from the second device for fermenting        the organic material under either mesophilic fermentation        conditions and/or thermophilic fermentation, said fermentation        resulting in the production of biogas comprising mainly methane        and/or    -   b) at least one tank for collection of biogas, wherein the tank        is optionally connected to an outlet for distribution of biogas,        or connected to a gas engine, and/or    -   c) at least one first separator, preferably a decanter        centrifuge in which the fermented material from the at least one        biogas fermenter is separated into an essentially liquid        fraction in the form of reject water, and an essentially solid        fraction, wherein said solid fraction comprises solid        phosphor (P) comprising organic and inorganic material, and/or    -   d) at least one second separator, preferably a ceramic        micro-filter in which the reject water from the at least one        first separator is further processed, preferably by aeration and        filtration, wherein said processing results in removing at least        some and preferably a majority of one or more of odour        components, nitrogen (N) compounds and potassium (K) compounds,        wherein said separation further results in the generation of        reject water comprising a reduced amount of any one or more of        odour components, nitrogen (N) compounds and potassium (K)        compounds as compared to the amount prior to separation.

The system preferably comprises pipe lines constituting a closed systempreventing or leading to a reduction in emissions of any one or more ofdust, microbial organisms, ammonia, air, liquid or any other constituentwithin the system.

Liquid fractions or reject water from one or more of the at least onesilage tank, the at least one pre-treatment fermenting tank, the atleast one biogas fermentor, the at least one first separator and the atleast one second separator is preferably re-used for cleaning of theanimal house or the stable.

The liquid fractions or reject water from any one or more of the atleast one silage tank, the at least one pretreatment fermenting tank,the at least one biogas fermentor, the at least one first separator andthe at least one second separator is preferably re-used in any step ofthe slurry separation and biogas production system to maintain theorganic material in a proper fluid condition.

The system makes it possible to add lime, including CaO and/or Ca(OH)₂,to the organic material before said organic material enters the strippertank for stripping N including ammonia, preferably by adding an amountof lime sufficient to generate a pH value of from about 10 to about 12,optionally in combination with a heating step and an aeration of theslurry including the organic material.

The organic material preferably remains in the stripper tank of thesystem for a period of 5 to 10 days, such as 7 days. The temperatureinside the stripper tank is preferably between 60° C. and 80° C. Anamount of from about 30 and 60 gram Ca(OH)₂ per kg dry matter in theorganic material is preferably added to the organic material in thestripper tank or before said organic material enters the stripper tank.

The system facilitates collection of stripped N including ammonia fromthe stripper tank and diversion of said stripped N to a column in whichN including ammonia is absorbed in water or an acid solution preferablycomprising sulphuric acid, and optionally also storing the absorbedammonia in a tank. The N absorbed in water or an acid solution in thisway is preferably used as a fertiliser.

The lime pressure cooker of the system is preferably an apparatus whichis initially capable of cutting the organic material into segments andsubsequently capable of diverting the segmented organic material to achamber wherein said segmented organic material is heated andsimultaneously exposed to a high pressure due to the elevatedtemperature. The organic material to be treated in the lime pressurecooker is added an amount of lime, including CaO and/or Ca(OH)₂, priorto or after entry into the lime pressure cooker.

Preferably CaO is added to the lime pressure cooker in an amount of from5-10 g per kg dry matter in the organic material. The system operates ata temperature of between 100° C. and 220° C., such as e.g. 180° C. to200° C. The temperature is aligned according to the organic material tobe treated, a higher temperature is chosen the higher the content ofcellulose, hemicellulose and lignin is in the organic material, or ahigher temperature is chosen according to the risk of infectiousmicrobial organism or pathogenic compounds including BSE prions in theorganic material.

The pressure is between preferably between from 2 to preferably lessthan 16 bar, such as from 4 to preferably less than 16 bar, for examplefrom 6 to preferably less than 16 bar, such as from 10 to preferablyless than 16 bar. The system operates at the elevated temperature forabout 5 to 10 minutes, but longer treatment times can also be used.

N including ammonia stripped in the lime pressure cooker is preferablycollected and diverted to a column and absorbed as described hereinelsewhere.

The system in one embodiment facilitates diversion of silage such ase.g. maize, energy crops, beets, and/or crop residues, to a mesophilicor thermophilic fermentation tank, before the material is furtherdiverted to the stripper tank.

The system can also facilitate diversion of lime pressure cooked organicmaterial to a mesophilic or thermophilic fermentation tank, before thematerial is diverted to the stripper tank.

The system also facilitates the optimization of the fermentation of theorganic material and the production of biogas by providing apre-treatment plant comprising facilities for stripping N includingammonia and/or performing alkaline hydrolysis under predeterminedprocess parameters, including pH level, temperature, aeration, duration,foam inhibition and flocculation of suspended material.

The system in another embodiment ensures optimised conditions for thepopulation of microbial organisms contained in the biogas producingfermenters. This is achieved by e.g. diverting sterilised or sanitisedslurry from the stripper tank to at least a first biogas fermenter,wherein said sterilised or sanitised slurry do not inhibit or harm thepopulation of biogas producing microbial organism in the fermenter. Inparticular, organic material from which N including ammonia is stripped,can be diverted to a biogas reactor in which the fermentation conditionssupports a mesophilic fermentation. Once the organic material has beensubjected to a mesophilic fermentation, the organic material ispreferably diverted to another biogas reactor of the system, in whichthe fermentation conditions are capable of supporting a thermophilicfermentation.

The thermophilic reaction conditions include a reaction temperatureranging from about 45° C. to 75° C., such as a reaction temperatureranging from about 55° C. to 60° C. The mesophilic reaction conditionsinclude a reaction temperature ranging from about 20° C. to 45° C.,including a reaction temperature ranging from about 30° C. to 35° C.

The system allows for both the thermophilic reaction and the mesophilicreaction to occur for about or at least 5-15 days, such as for about orat least 7-10 days, preferably at least 7 days.

The system comprises devices capable of preventing foam formation,wherein said devices are capable of adding e.g. polymers, and/or plantoils, including rape oil, and/or different salts, including saltscomprising CaO and/or Ca(OH)₂.

The system makes it possible to reuse at least part of the fermentedorganic material from the biogas reactors in that same reactor, whereinsaid fermented organic material functions as an inoculum of thepopulation of microbial organism performing the fermentation.

The system makes it possible in one embodiment to divert a slurryincluding a liquid comprising solid parts, to a first separator forseparating the solid materials including a limited fraction of theliquid from the main part of the liquid fraction. Said mainly solidfraction comprises organic and inorganic material including P (phosphor)and compounds hereof. Said mainly solid fraction can be further driedand comprises a fertiliser. The first separator of the system ispreferably a decanter centrifuge.

The system also allows reject water from the first separator to betreated in a second separator, said second separator comprising aceramic micro-filters in which the reject water from the first separatoris further processed by aeration and filtration, optionally removing anyresidual odour components, any residual nitrogen compounds and/or anycomponents containing K (potassium), leaving an essentially clean rejectwater comprising essentially none of said residual components.

The system makes it possible to divert the reject water from thethermophilic biogas reactor or from the first and/or second separator toan agricultural field, to a waste water treatment plant, or a purifyingplant, or a biological treatment plant for further purification ifrequired.

The system or the methods of the present invention can be used to:

eliminate or decline the emission to the environment of dust, microbialorganisms, ammonia, contaminated air, liquid or any other constitutionwithin the system, especially from animal houses.

improve the utilisation of the energy contained in a biomass includingorganic material.

improve the production of biogas comprising methane gas andmethane-bearing gas. Said gas may be stored in a tank locally and/or canbe diverted to a commercial net of distributing gas.

obtain separate fractions of N (nitrogen), P (phosphor) and potentiallyK (potassium) from organic materials. Said fractions are of commercialvalue and can be utilised as fertilisers to fertilise agricultural andhorticultural crops.

obtain an improved animal welfare and improved hygiene in animal stablesand in accordance to output from said animal stables. Said outputcomprising manure, slurry and animals to be slaughtered. The cleananimals reduces the risk of infection of meat when the animals areslaughtered.

-   obtain a procedure for rendering animal carcasses or fractions    hereof, meat and bone meal or any other produce from animals    available for disposing off to agricultural land in the form of    refined fertilizers and thus to benefit from micro- and    macro-nutrients in the animal produce in the agricultural or    horticultural plant production.

1. A method for producing a processed organic material characterized bya reduced number of viable microbial organisms, infectious agents,and/or prions relative to that present in an organic material from whichit is derived, and for producing biogas from at least some of saidprocessed organic material, said method comprising the steps of i.providing an organic material comprising solid parts or solid and liquidparts, wherein said organic material comprises viable microbialorganisms, infectious agents, prions, or combinations thereof, andwherein said solid parts comprise a plant material, an animal material,or a combination thereof, said plant material comprising cellulose,hemicellulose, lignin, or combinations thereof and said animal materialcomprising slaughterhouse waste, meat, bone meal, or combinationsthereof; ii. subjecting said organic material, to the processing stepsof: a. lime pressure cooking under pressure at a temperature of 120° C.to 250° C. and a pH-value of above 9 obtained at least in part by addinglime prior to or during said lime pressure cooking, said lime pressurecooking resulting in hydrolysis of the organic material, wherein whensaid organic material comprises plant material said lime pressurecooking further comprises hydrolysis of the cellulose, hemicellulose,and/or lignin of said solid parts, wherein the lime is Ca(OH)2 and/orCaO; and b. stripping ammonia from said lime pressure cooked organicmaterial, thereby obtaining a processed organic material comprising areduced number of viable microbial organisms, infectious agents and/orprions, and further comprising hydrolysed solid parts of the providedorganic material of step (i); iii. directing at least some of theprocessed organic material comprising hydrolysed solid parts of organicmaterial to one or more biogas fermenters; iv. fermenting the processedorganic material in the one or more biogas fermenters, thereby producinga biogas; and v. obtaining the biogas from the biogas fermenter.
 2. Themethod of claim 1, wherein said microbial organisms are veterinarymicrobial and zoonotic pathogens.
 3. The method of claim 1, wherein saidmicrobial organisms are selected from infectious microbial organisms andparasitic pathogen microbial organisms.
 4. The method of claim 1,wherein said organic material comprising said solid parts or said solidand liquid parts is selected from the group consisting of a cropresidue, a silage crop, an animal carcass or a portion thereof, a manureor slurry thereof, said slaughterhouse waste, said meat, said bone meal,and combinations thereof.
 5. The method of claim 1, further comprising(ii) (a′) fermenting at least some of the lime pressure cooked organicmaterial prior to the stripping ammonia step (ii) (b).
 6. The method ofclaim 1, said organic material of step (i) comprising organic materialof plant origin, and said method further comprising ensiling the organicmaterial of plant origin before the stripping ammonia step (ii) (b). 7.The method of claim 6, further comprising fermenting the ensiled organicmaterial prior to the stripping ammonia step (ii) (b).
 8. The method ofclaim 1, wherein the step (ii) (b) of stripping ammonia is performed ata pH value above 9 and a temperature above 40° C.
 9. The method of claim8, wherein the pH value in the stripping ammonia step (ii) (b) is above10.
 10. The method of claim 8, wherein the pH value in the strippingammonia step (ii) (b) is above
 11. 11. The method of claim 8, whereinthe stripping ammonia temperature is above 50° C.
 12. The method ofclaim 8, wherein the stripping ammonia temperature is above 60° C. 13.The method of claim 8, wherein the operation time of the strippingammonia step (ii) (b) is from 2 to 15 days.
 14. The method of claim 8,wherein the operation time of the stripping ammonia step (ii) (b) isfrom 4 to 10 days.
 15. The method of claim 8, wherein the operation timeof the stripping ammonia step (ii) (b) is from 6 to 8 days.
 16. Themethod of claim 8, wherein the organic material of step (i) comprises amaximum of 500 (w/v) solid parts.
 17. The method of claim 8, wherein theorganic material of step (i) comprises a maximum of 30% (w/v) solidparts.
 18. The method of claim 8, wherein the organic material of step(i) comprises a maximum of 10% (w/v) solid parts.
 19. The method ofclaim 8, further comprising absorbing the stripped ammonia in a columnand then storing the column-absorbed, stripped ammonia in a tank. 20.The method of claim 19, wherein the column comprises water or an acidicsolution.
 21. The method of claim 20, wherein the acidic solution issulphuric acid.
 22. The method of claim 1, wherein in step (ii) (a) thelime pressure cooking of the organic material is performed at atemperature of from 120° C. to 220° C., at a pressure of 2 to 20 bar,with addition of lime sufficient to reach a pH value of from above 9 upto 12, and with an operation time of the step of lime pressure cookingof from at least 1 minute to less than 60 minutes.
 23. The method ofclaim 22, wherein, in the lime pressure cooking step (ii) (a), thetemperature is in the interval of 180° C. to 200° C., wherein thepressure is from 10 bar to less than 16 bar, wherein the pH value isfrom 10 to 12, and wherein the operation time of the step of limepressure cooking is from 5 minutes to 10 minutes.
 24. The method ofclaim 22, wherein the organic material further comprises deep litter ormanure from cattle, pigs and poultry.
 25. The method of claim 22,wherein the organic material further comprises proteins constitutingbovine spongiform encephalopathy (BSE) prions or other prions, whereinsaid BSE prions or other prions are substantially reduced or eliminatedin the lime pressure cooking step.
 26. The method of claim 22, whereinsaid solid parts of the provided organic material of (i) comprise saidplant material in a form selected from the group consisting of straw,fibres or sawdust.
 27. The method of claim 22, wherein the providedorganic material has a content of fibres of more than 10% (w/w).
 28. Themethod of claim 22, wherein the provided organic material has a contentof complex carbohydrates comprising said cellulose and/or saidhemicellulose and/or said lignin, of more than 101 (w/w).
 29. The methodof claim 22, wherein the lime pressure cooking step (ii) (a) comprisesadding the CaO in an amount of from 2 to 80 g per kg dry matter of theprovided organic material of (i).
 30. The method of claim 22, whereinthe lime pressure cooking step (ii) (a) comprises adding the CaO in anamount of from 5 to 60 g per kg dry matter of the provided organicmaterial of (i).
 31. The method of claim 22, further comprisingmacerating the provided organic material before the lime pressurecooking step (ii) (a).
 32. The method of claim 31, further comprisingconveying the macerated organic material into a lime pressure cooker,wherein the macerating and conveying of the provided organic materialcomprises macerating and conveying by means of a screw conveyor equippedwith macerator; and in step (ii)(a) providing said lime pressure cookingby heating the conveyed organic material, wherein the heating comprisesproviding steam injection into the lime pressure cooker, providing steamin a cape around the lime pressure cooker, or by a combination thereof.33. The method of claim 22 comprising the further step (ii) (a′) offermenting, under mesophilic and/or thermophilic fermentationconditions, at least some of the organic material treated in the limepressure cooking step (ii) (a) before subjecting said organic materialto stripping ammonia step (ii) (b).
 34. The method of claim 33, whereinthe fermenting in step (ii) and/or step (iv) further comprisesfermenting by means of a bacterial population.
 35. The method of claim33, wherein the fermenting in step (ii) and/or step (iv) comprisesfermenting anaerobically.
 36. The method of claim 33, wherein theorganic material provided in (i) comprises said animal material, whereinsaid organic material contains an amount of nitrogen (N) of more than10% (w/v).
 37. The method of claim 33, wherein the fermenting in step(ii) (a′) is performed at a temperature of from 15° C. to less than 65°C.
 38. The method of claim 33, wherein the fermenting in step (ii) (a′)is performed at a temperature of from 25° C. to less than 55° C.
 39. Themethod of claim 33, wherein the fermenting in step (ii) (a′) isperformed at a temperature of from 35° C. to less than 45° C.
 40. Themethod of claim 33, wherein the fermenting in step (ii) (a′) isperformed for a period of time from 5 to less than 15 days.
 41. Themethod of claim 33, wherein the fermenting in step (ii) (a′) isperformed for a period of time from 7 to less than 10 days.
 42. Themethod of claim 6, wherein the organic material to be ensilagedcomprises annual fodder crops.
 43. The method of claim 1, wherein thefermenting comprises anaerobically fermenting in one or more biogasfermenters the processed organic material with biogas-producingmicrobial fermentation organisms.
 44. The method of claim 43, wherein instep (iv) the fermenting comprises producing biogas in two biogasfermenters by anaerobic bacterial fermentation of the organic material,comprising: a. fermenting the processed organic material at atemperature above 45° C. with biogas-producing fermentation bacteria ina first biogas fermenter; b. diverting the fermented processed organicmaterial to a second biogas fermenter; and then c. fermenting thediverted processed organic material with biogas-producing bacteria at atemperature below 45° C.
 45. The method of claim 44, wherein thetemperature in said first biogas fermenter is from 45° C. to 75° C. 46.The method of claim 44, wherein the temperature in said first biogasfermenter is from 55° C. to 60° C.
 47. The method of claim 44, whereinthe temperature in said second biogas fermenter is from 20° C. to 45° C.48. The method of claim 44, wherein the temperature in said secondbiogas fermenter is from 30° C. to 35° C.
 49. The method of claim 44,wherein the fermentation reaction in said first biogas fermenter isperformed for 5 to 15 days.
 50. The method of claim 44, wherein thefermentation reaction in said first biogas fermenter is performed for 7to 10 days.
 51. The method of claim 44, wherein the fermentationreaction in said second biogas fermenter is performed for 5 to 15 days.52. The method of claim 44, wherein the fermentation reaction in saidsecond biogas fermenter is performed for 7 to 10 days.
 53. The method ofclaim 44, further comprising adding at least one anti-foaming agent,selected from the group consisting of polymers, plant oils, and salts,in an amount effective to reduce or eliminate foam formation in saidfermenting step (iv).
 54. The method of claim 53, wherein the plant oilscomprise rape oil.
 55. The method of claim 43, wherein the fermenting instep (iv) further comprises adding calcium ions to the organic materialthereby flocculating substances and particles during biogas production,said calcium ions being capable of forming particulate, flock-formingcalcium bridges therein.
 56. The method of claim 55, the adding of thecalcium-ions further results in the precipitation of orthophosphates,including dissolved (PO₄)³⁻.
 57. The method of claim 1, furthercomprising directing the obtained biogas to a gas engine capable ofproducing heat therefrom, wherein the heat produced by the gas engine isused to provide heat in the lime pressure cooking, the ammoniastripping, the fermenting, or a combination thereof.
 58. The method ofclaim 1 wherein the microbial organisms and infectious agents includeCampylobacter, Salmonella, Yersinia, Ascaris, vira or viroids.
 59. Themethod of claim 1 further comprising the step of producing anitrogen-comprising fertiliser (N fertiliser) containing ammonia, saidproduction comprising the steps of i) collecting the ammonia strippedfrom the organic material in the stripping ammonia step, (ii) (b), ii)absorbing said collected ammonia in water or an acidic solutioncomprising sulphuric acid, and iii) obtaining the N-fertilisercontaining said ammonia.
 60. The method of claim 1 further comprisingthe step of producing phosphorus-comprising fertiliser (P-fertiliser),said production comprising the steps of i) diverting a slurry comprisingthe fermented organic material from said one or more biogas fermentersto a first separator, ii) separating said slurry into a solid fractionand a liquid fraction of reject water, iii) obtaining said solidfraction containing part of the phosphorus as calcium phosphate(Ca₃(PO₄)₂) and organic phosphates initially suspended in the slurry,wherein said solid fraction is capable of being used as a P-fertiliser.61. The method of claim 60, wherein the separator is a decantercentrifuge.
 62. The method of claim 60, further comprising drying thesolid fraction comprising phosphorus to produce a granulate comprising aP-fertiliser.
 63. The method of claim 60, wherein the reject waterobtained from the separation step has a content of nitrogen (N) andphosphorus (P) of less than 0.1% (w/v).
 64. The method of claim 63,further comprising diverting the reject water to the stripping ammoniastep and re-using said reject water for stripping ammonia from organicmaterial.
 65. The method of claim 63, wherein reject water is reusablefor cleaning a stable.
 66. The method of claim 63, wherein the rejectwater is free from sources capable of spreading zoonoses, veterinaryvira, infectious bacteria, parasites, ESE prions and other prions. 67.The method of claim 60 comprising the further steps of stripping theammonia from said reject water in a steam stripper.
 68. The method ofclaim 67, further comprising condensing the stripped ammonia in a twostep condensator.
 69. The method of claim 68, wherein ammonia iscondensed in a first step in a counter current of cooled ammoniacondensate.
 70. The method of claim 69, wherein ammonia not condensed inthe first step is condensed in a counter current of permeate from areverse osmosis step used for extracting potassium (K) from the rejectwater.
 71. The method of claim 67 comprising the further step ofdiverting the stripped ammonia to the column on which ammonia from thefirst ammonia stripper tank is absorbed.
 72. The method of claim 60comprising the further step of producing a potassium-comprisingfertiliser (K-fertiliser) from the organic material, said productioncomprising i) diverting the potassium-comprising liquid fraction ofreject water from the first separation step to a second separation step,ii) separating the remaining organic and inorganic composition from theliquid fraction, and iii) obtaining a liquid concentrate comprisingpotassium, wherein said liquid concentrate comprising potassium iscapable of being used as a K-fertiliser.
 73. The method of claim 72,wherein the second separation step comprises subjecting thepotassium-comprising liquid fraction through a micro filter operatingwith an intermittent aeration and filtration of the reject water,wherein said aeration provides decomposition of the remaining organicmaterial and settling of inorganic flocks.
 74. The method of claim 1,wherein, in step (iii) the processed organic material directed to thebiogas fermenter is a slurry comprising the hydrolysed solid parts and aliquid.
 75. The method of claim 1 wherein the pressure cooking is at atemperature of between 120° C. and 220° C.
 76. The method of claim 1wherein the lime pressure cooking is at a temperature of at least 140°C., a pressure of at least 4 bar, and a pH of at least about
 10. 77. Themethod of claim 76 wherein the lime pressure cooking is at a temperatureof 140-180° C., a pressure of 4-8 bar, and a pH of about 10-12.
 78. Themethod of claim 77 wherein the provided organic matter comprises BSEprions and wherein the BSE prions are at least partially hydrolyzed as aresult of said lime pressure cooking.
 79. The method of claim 78wherein, as a result of said stripping ammonia, the processed organicmaterial diverted to said biogas fermenter has a lower ratio of nitrogento carbon than did the organic material provided in step (i), andconsequently the fermentation organisms in said one or more biogasfermenters fermenter produce additional extracellular proteinases andproteases capable of hydrolyzing the BSE prions than said fermentationorganisms would if the ratio of nitrogen to carbon hadn't been reduced.80. The method of claim 1 wherein the hydrolysis of cellulose,hemicellulose and/or lignin occurring in step (ii) (a) is substantiallygreater than that which would occur if that step were performed at 100°C.
 81. The method of claim 1 wherein the production of biogas issubstantially greater than that which would occur if step (ii) (a) wereperformed at 100° C.
 82. The method of claim 1 wherein the organicmaterial provided in step (i) comprises animal organic material.
 83. Themethod of claim 82 wherein the animal organic material comprises manure.84. The method of claim 1 wherein the temperature of the lime pressurecooking step (ii) (a) is less than that which causes substantialpyrolysis of the organic material to produce gases andpolycyclic-aromatic hydrocarbons (PAH).
 85. The method of claim 1wherein said solid parts of the organic material provided in step (i)comprise cellulose and/or hemicellulose and/or lignin.
 86. The method ofclaim 1 wherein at least some orthophosphate dissolved in said organicmaterial is precipitated during said lime pressure cooking step (ii)(a).
 87. The method of claim 1, wherein the stripping ammoniatemperature is above 50° C.
 88. The method of claim 1, wherein thestripping ammonia temperature is above 60° C.
 89. The method of claim 1,wherein the operation time of the stripping ammonia step (ii) (b) isfrom 2 to 15 days.
 90. The method of claim 1, wherein the operation timeof the stripping ammonia step (ii) (b) is from 4 to 10 days.
 91. Themethod of claim 1, wherein the operation time of the stripping ammoniastep (ii) (b) is from 6 to 8 days.
 92. The method of claim 1, whereinthe organic material of step (i) comprises a maximum of 500 (w/v) solidparts.
 93. The method of claim 1, wherein the organic material of step(i) comprises a maximum of 30% (w/v) solid parts.
 94. The method ofclaim 1, wherein the organic material of step (i) comprises a maximum of10% (w/v) solid parts.
 95. The method of claim 1, further comprisingabsorbing the stripped ammonia in a column and then storing said ammoniain a tank.
 96. The method of claim 85, wherein the step (ii) (b) ofstripping ammonia is performed at a pH value above 9 and a temperatureabove 40° C.
 97. The method of claim 96, wherein the pH value in thestripping ammonia step (ii) (b) is above
 10. 98. The method of claim 96,wherein the pH value in the stripping ammonia step (ii) (b) is above 11.99. The method of claim 1, wherein the operation time of the strippingammonia step (ii) (b) is from 4 to 10 days.
 100. The method of claim 1,wherein the operation time of the stripping ammonia step (ii) (b) isfrom 6 to 8 days.
 101. The method of claim 1, wherein the organicmaterial of step (i) comprises a maximum of 50% (w/v) solid parts. 102.The method of claim 85, wherein the step (ii) (a) of lime pressurecooking the organic material is performed at a temperature of from 120°C. to 220° C., at a pressure of 2 to 20 bar, with addition of limesufficient to reach a pH value of from above 9 up to 12, and with anoperation time of the step of lime pressure cooking of from at least 1minute to less than 60 minutes.
 103. The method of claim 102, wherein,in the lime pressure cooking step a), the temperature is in the intervalof 180° C. to 200° C., wherein the pressure is from 10 bar to less than16 bar, wherein the pH level is from 10 to 12, and wherein the operationtime of the step of lime pressure cooking is from 5 minutes to 10minutes.
 104. The method of claim 102, wherein the provided organicmaterial has a content of fibres of more than 10% (w/w).
 105. The methodof claim 85 wherein the lime pressure cooking step (ii) (a) is at atemperature of between 120° C. and 220° C.
 106. The method of claim 85wherein the lime pressure cooking step (ii) (a) is at a temperature ofat least 140° C., a pressure of at least 4 bar, and a pH of at leastabout
 10. 107. The method of claim 85 wherein the lime pressure cookingstep (ii) (a) is at a temperature of 140-180° C., a pressure of 4-8 bar,and a pH of about 10-12.